Phase 5: Offline downloads at selectable bitrates

Adds Room + WorkManager-backed offline downloads: a bitrate picker
(Low/Normal/High/Original) on track and album detail screens, a
Downloads library screen, and Settings additions for Wi-Fi-only
downloads and default quality. Bitrate tiers route through Subsonic's
`stream` endpoint with `maxBitRate`; Original uses `download`, which
always returns the untranscoded source file.

Three real bugs found and fixed during on-device verification:

- WorkManager was constructing DownloadWorker with its default
  reflection-based WorkerFactory instead of HiltWorkerFactory
  (NoSuchMethodException on the @AssistedInject constructor). The
  default androidx.startup auto-init ran before Hilt's field
  injection was guaranteed to have happened. Fixed by disabling the
  manifest's auto-init provider and calling WorkManager.initialize()
  manually in DeepwaveApplication.onCreate(), after super.onCreate().

- Crash on every download: WorkManager's own SystemForegroundService
  declares no foregroundServiceType in its manifest, but the worker
  requests dataSync at runtime via ForegroundInfo, which API 29+
  requires to be a subset of what's manifest-declared. Fixed by
  manifest-merging that service with foregroundServiceType="dataSync".

- Offline playback was completely broken: ResolvingDataSource only
  rewrites the DataSpec's URI (to file:// for a downloaded track) but
  always hands it to the same wrapped upstream DataSource to open.
  OkHttpDataSource can only open http(s) URLs, so the rewritten
  file:// URI failed with "Malformed URL" and playback silently fell
  through to the network. Wrapping the signed OkHttpDataSource.Factory
  in DefaultDataSource.Factory routes by scheme instead - this bug was
  latent since Phase 4, since LocalTrackFiles was always empty until
  now and the local-file path was never actually exercised.

- Re-downloading a track at a different quality could produce a
  different file extension (Content-Type-driven), orphaning the
  previous file on disk with no cleanup path. DownloadWorker now
  clears any existing files for the track id before writing the new
  one.

Verified on-device: downloads at all four tiers produce distinctly
different, correctly-ordered file sizes (Low < Normal < High <
Original); a fully downloaded track keeps playing with Wi-Fi and
mobile data both disabled; killing and relaunching the app mid-download
lets WorkManager resume the interrupted download to a correct,
byte-exact final file.

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

app/build.gradle.kts

@@ -56,6 +56,8 @@ dependencies {
     implementation(libs.hilt.android)
     ksp(libs.hilt.compiler)
     implementation(libs.androidx.hilt.lifecycle.viewmodel.compose)
+    implementation(libs.androidx.hilt.work)
+    ksp(libs.androidx.hilt.compiler)
 
     // Networking (Subsonic/Navidrome API client)
     implementation(libs.retrofit)
@@ -77,10 +79,18 @@ dependencies {
     implementation(libs.androidx.media3.session)
     implementation(libs.androidx.media3.datasource.okhttp)
 
+    // Offline downloads (Room index + WorkManager)
+    implementation(libs.androidx.room.runtime)
+    implementation(libs.androidx.room.ktx)
+    ksp(libs.androidx.room.compiler)
+    implementation(libs.androidx.work.runtime.ktx)
+
     testImplementation(libs.junit)
     testImplementation(libs.okhttp.mockwebserver)
     testImplementation(libs.mockito.core)
     testImplementation(libs.kotlinx.coroutines.test)
+    testImplementation(libs.androidx.room.testing)
+    testImplementation(libs.androidx.work.testing)
     androidTestImplementation(platform(libs.androidx.compose.bom))
     androidTestImplementation(libs.androidx.compose.ui.test.junit4)
     androidTestImplementation(libs.androidx.espresso.core)