Bootstrap Castarr from NodeCast prototype

Imported the native TV app (Kotlin, ExoPlayer, embedded remote server, QR
pairing) plus CONTEXT.md and ADRs 0001-0005. Rename, Compose for TV UI and
the Dispatcharr integration follow as tracked issues.

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

.github/workflows/build.yml

@@ -0,0 +1,27 @@
+name: Build TV app
+
+on:
+  push:
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: "17"
+
+      - uses: gradle/actions/setup-gradle@v4
+
+      - name: Build debug APK
+        run: ./gradlew assembleDebug --stacktrace
+
+      - name: Upload APK
+        uses: actions/upload-artifact@v4
+        with:
+          name: castarr-debug-apk
+          path: app/build/outputs/apk/debug/app-debug.apk