Live screen: group rail layout, exclusive filtering, cleaner top bar

- Groups live in a scrollable rail on the left (Alle Sender, Favoriten,
  then Dispatcharr groups with counts); focusing one opens it like a
  menu — filters no longer stack additively.
- Channel list sits right of the rail with Now/Next and progress;
  group subline only shown in the Alle view.
- Top bar: wordmark plus one context pill (Einstellungen / Zurück zu
  Live) instead of two text tabs; Back returns to Live instead of
  quitting the app.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/src/main/java/dev/castarr/tv/ui/CastarrApp.kt

@@ -27,6 +27,14 @@ import dev.castarr.tv.AppState
 
 @Composable
 fun CastarrApp(state: AppState) {
+    // Back always leads home instead of quitting the app by accident.
+    androidx.activity.compose.BackHandler(
+        enabled = !state.playerVisible && state.screen != AppState.Screen.LIVE
+            && state.screen != AppState.Screen.WELCOME
+    ) {
+        state.screen = if (state.screen == AppState.Screen.ADVANCED) AppState.Screen.SETTINGS
+        else AppState.Screen.LIVE
+    }
     Box(
         modifier = Modifier
             .fillMaxSize()
@@ -65,14 +73,6 @@ private fun TopBar(state: AppState) {
             fontWeight = FontWeight.Medium,
             letterSpacing = 4.sp,
         )
-        Spacer(Modifier.width(36.dp))
-        TabItem("Live", state.screen == AppState.Screen.LIVE) {
-            state.screen = AppState.Screen.LIVE
-        }
-        Spacer(Modifier.width(10.dp))
-        TabItem("Einstellungen", state.screen == AppState.Screen.SETTINGS) {
-            state.screen = AppState.Screen.SETTINGS
-        }
         Spacer(Modifier.weight(1f))
         state.connectedRemote?.let { name ->
             Row(verticalAlignment = Alignment.CenterVertically) {
@@ -85,6 +85,14 @@ private fun TopBar(state: AppState) {
                 Spacer(Modifier.width(8.dp))
                 Text(name, color = CastarrColors.muted, fontFamily = AppFont, fontSize = 13.sp)
             }
+            Spacer(Modifier.width(18.dp))
+        }
+        TabItem(
+            if (state.screen == AppState.Screen.LIVE) "⚙  Einstellungen" else "‹  Zurück zu Live",
+            selected = false,
+        ) {
+            state.screen = if (state.screen == AppState.Screen.LIVE) AppState.Screen.SETTINGS
+            else AppState.Screen.LIVE
         }
     }
 }

app/src/main/java/dev/castarr/tv/ui/LiveScreen.kt

@@ -6,6 +6,7 @@ import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxHeight
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
@@ -13,7 +14,6 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.LazyColumn
-import androidx.compose.foundation.lazy.LazyRow
 import androidx.compose.foundation.lazy.items
 import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.foundation.shape.RoundedCornerShape
@@ -23,6 +23,7 @@ import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
+import androidx.compose.ui.focus.onFocusChanged
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextOverflow
@@ -36,6 +37,10 @@ import dev.castarr.tv.AppState
 import dev.castarr.tv.data.NowNext
 import dev.castarr.tv.playlist.Channel
 
+/**
+ * Live tab: group rail on the left (focusing a group opens it — exclusive,
+ * like a menu), channels of the open group with Now/Next on the right.
+ */
 @Composable
 fun LiveScreen(state: AppState) {
     val genericChannels by state.source.channels.collectAsStateWithLifecycle()
@@ -50,9 +55,11 @@ fun LiveScreen(state: AppState) {
     val groups = remember(allChannels) {
         allChannels.mapNotNull { it.group.ifEmpty { null } }.distinct().sorted()
     }
-    val channels = allChannels
-        .let { list -> if (isDispatcharr && state.favoritesOnly) list.filter { it.backendId in favorites } else list }
-        .let { list -> state.groupFilter?.let { g -> list.filter { it.group == g } } ?: list }
+    val channels = when {
+        state.favoritesOnly -> allChannels.filter { it.backendId in favorites }
+        state.groupFilter != null -> allChannels.filter { it.group == state.groupFilter }
+        else -> allChannels
+    }
 
     if (allChannels.isEmpty()) {
         Box(Modifier.fillMaxSize(), contentAlignment = Alignment.Center) {
@@ -66,73 +73,136 @@ fun LiveScreen(state: AppState) {
         return
     }
 
-    Column(Modifier.fillMaxSize()) {
-    LazyRow(
-        modifier = Modifier.padding(bottom = 6.dp),
-        contentPadding = androidx.compose.foundation.layout.PaddingValues(horizontal = 40.dp),
-        horizontalArrangement = Arrangement.spacedBy(8.dp),
-    ) {
-        item {
-            FilterChip("Alle", !state.favoritesOnly && state.groupFilter == null) {
-                state.favoritesOnly = false
-                state.groupFilter = null
-            }
-        }
-        if (isDispatcharr) {
+    Row(Modifier.fillMaxSize()) {
+        LazyColumn(
+            modifier = Modifier
+                .width(264.dp)
+                .fillMaxHeight(),
+            contentPadding = androidx.compose.foundation.layout.PaddingValues(
+                start = 28.dp, end = 12.dp, top = 4.dp, bottom = 32.dp
+            ),
+            verticalArrangement = Arrangement.spacedBy(2.dp),
+        ) {
             item {
-                FilterChip("★ Favoriten", state.favoritesOnly) {
-                    state.favoritesOnly = !state.favoritesOnly
+                GroupItem(
+                    label = "Alle Sender",
+                    count = allChannels.size,
+                    selected = !state.favoritesOnly && state.groupFilter == null,
+                ) {
+                    state.favoritesOnly = false
+                    state.groupFilter = null
+                }
+            }
+            if (isDispatcharr) {
+                item {
+                    GroupItem(
+                        label = "★ Favoriten",
+                        count = favorites.size,
+                        selected = state.favoritesOnly,
+                    ) {
+                        state.favoritesOnly = true
+                        state.groupFilter = null
+                    }
+                }
+            }
+            item {
+                Box(
+                    Modifier
+                        .padding(horizontal = 14.dp, vertical = 8.dp)
+                        .fillMaxWidth()
+                        .height(1.dp)
+                        .background(CastarrColors.line)
+                )
+            }
+            items(groups, key = { it }) { group ->
+                GroupItem(
+                    label = group,
+                    count = remember(allChannels, group) { allChannels.count { it.group == group } },
+                    selected = state.groupFilter == group,
+                ) {
+                    state.favoritesOnly = false
+                    state.groupFilter = group
                 }
             }
         }
-        items(groups, key = { it }) { group ->
-            FilterChip(group, state.groupFilter == group) {
-                state.groupFilter = if (state.groupFilter == group) null else group
+
+        LazyColumn(
+            modifier = Modifier
+                .weight(1f)
+                .fillMaxHeight(),
+            contentPadding = androidx.compose.foundation.layout.PaddingValues(
+                start = 8.dp, end = 40.dp, top = 4.dp, bottom = 32.dp
+            ),
+            verticalArrangement = Arrangement.spacedBy(4.dp),
+        ) {
+            if (channels.isEmpty()) {
+                item {
+                    Text(
+                        if (state.favoritesOnly)
+                            "Noch keine Favoriten — halte OK auf einem Sender gedrückt."
+                        else "Diese Gruppe ist leer.",
+                        color = CastarrColors.faint,
+                        fontFamily = AppFont,
+                        fontSize = 14.sp,
+                        modifier = Modifier.padding(24.dp),
+                    )
+                }
+            }
+            items(channels, key = { it.url + it.name }) { channel ->
+                ChannelRow(
+                    channel = channel,
+                    index = channels.indexOf(channel),
+                    showGroup = state.groupFilter == null,
+                    nowNext = state.nowNext(channel),
+                    playing = state.currentChannel?.url == channel.url,
+                    favorite = isDispatcharr && channel.backendId in favorites,
+                    epgStamp = epgStamp,
+                    onLongClick = if (isDispatcharr) {
+                        { state.dispatcharr.toggleFavorite(channel) }
+                    } else null,
+                ) { state.play(channel) }
             }
         }
     }
-    LazyColumn(
-        modifier = Modifier.fillMaxSize(),
-        contentPadding = androidx.compose.foundation.layout.PaddingValues(
-            start = 40.dp, end = 40.dp, top = 8.dp, bottom = 32.dp
-        ),
-        verticalArrangement = Arrangement.spacedBy(4.dp),
-    ) {
-        items(channels, key = { it.url + it.name }) { channel ->
-            ChannelRow(
-                channel = channel,
-                index = channels.indexOf(channel),
-                nowNext = state.nowNext(channel),
-                playing = state.currentChannel?.url == channel.url,
-                favorite = isDispatcharr && channel.backendId in favorites,
-                epgStamp = epgStamp,
-                onLongClick = if (isDispatcharr) {
-                    { state.dispatcharr.toggleFavorite(channel) }
-                } else null,
-            ) { state.play(channel) }
-        }
-    }
-    }
 }
 
 @Composable
-private fun FilterChip(label: String, selected: Boolean, onClick: () -> Unit) {
+private fun GroupItem(label: String, count: Int, selected: Boolean, onSelect: () -> Unit) {
     Surface(
-        onClick = onClick,
-        shape = ClickableSurfaceDefaults.shape(RoundedCornerShape(999.dp)),
+        // Focusing a group opens it right away (browse like a menu);
+        // clicking is not required, but harmless.
+        onClick = onSelect,
+        modifier = Modifier
+            .fillMaxWidth()
+            .onFocusChanged { if (it.isFocused) onSelect() },
+        shape = ClickableSurfaceDefaults.shape(RoundedCornerShape(10.dp)),
         colors = ClickableSurfaceDefaults.colors(
-            containerColor = if (selected) CastarrColors.accentDim else CastarrColors.surface,
+            containerColor = if (selected) CastarrColors.accentDim else Color.Transparent,
             contentColor = if (selected) CastarrColors.accent else CastarrColors.muted,
             focusedContainerColor = CastarrColors.accent,
             focusedContentColor = CastarrColors.onAccent,
         ),
     ) {
-        Text(
-            label,
-            fontFamily = AppFont,
-            fontSize = 12.sp,
-            modifier = Modifier.padding(horizontal = 14.dp, vertical = 6.dp),
-        )
+        Row(
+            modifier = Modifier.padding(horizontal = 14.dp, vertical = 9.dp),
+            verticalAlignment = Alignment.CenterVertically,
+        ) {
+            Text(
+                label,
+                fontFamily = AppFont,
+                fontSize = 14.sp,
+                fontWeight = if (selected) FontWeight.Medium else FontWeight.Normal,
+                maxLines = 1,
+                overflow = TextOverflow.Ellipsis,
+                modifier = Modifier.weight(1f),
+            )
+            Spacer(Modifier.width(8.dp))
+            Text(
+                "$count",
+                fontFamily = AppFont,
+                fontSize = 12.sp,
+            )
+        }
     }
 }
 
@@ -140,6 +210,7 @@ private fun FilterChip(label: String, selected: Boolean, onClick: () -> Unit) {
 private fun ChannelRow(
     channel: Channel,
     index: Int,
+    showGroup: Boolean,
     nowNext: NowNext,
     playing: Boolean,
     favorite: Boolean,
@@ -189,7 +260,7 @@ private fun ChannelRow(
                     maxLines = 1,
                     overflow = TextOverflow.Ellipsis,
                 )
-                if (channel.group.isNotEmpty()) {
+                if (showGroup && channel.group.isNotEmpty()) {
                     Text(
                         channel.group,
                         color = CastarrColors.faint,