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/src/main/res/values/strings.xml

@@ -17,6 +17,22 @@
 
     <string name="settings_title">Settings</string>
     <string name="settings_log_out">Log out</string>
+    <string name="settings_downloads">Downloads</string>
+    <string name="settings_wifi_only_downloads">Download over Wi-Fi only</string>
+    <string name="settings_default_quality">Default download quality</string>
+
+    <string name="download_notification_channel_name">Downloads</string>
+    <string name="download_notification_title">Downloading</string>
+    <string name="download_pick_quality">Download quality</string>
+    <string name="download_album">Download album</string>
+    <string name="download_action">Download</string>
+    <string name="download_downloading">Downloading</string>
+    <string name="download_downloaded">Downloaded</string>
+    <string name="download_failed">Download failed, tap to retry</string>
+    <string name="download_remove">Remove download</string>
+
+    <string name="downloads_title">Downloads</string>
+    <string name="downloads_empty">No downloads yet</string>
 
     <string name="player_nothing_playing">Nothing playing</string>
     <string name="player_play">Play</string>

app/src/main/res/xml/backup_rules.xml

@@ -8,4 +8,7 @@
 <full-backup-content>
     <exclude domain="sharedpref" path="deepwave_master_keyset_prefs.xml"/>
     <exclude domain="file" path="datastore/deepwave_credentials.preferences_pb"/>
+    <!-- Restoring "downloaded" rows without the actual audio files (app-specific external
+         storage, never backed up) would be misleading state - the DB and files must move together. -->
+    <exclude domain="database" path="deepwave.db"/>
 </full-backup-content>

app/src/main/res/xml/data_extraction_rules.xml

@@ -7,9 +7,11 @@
     <cloud-backup>
         <exclude domain="sharedpref" path="deepwave_master_keyset_prefs.xml"/>
         <exclude domain="file" path="datastore/deepwave_credentials.preferences_pb"/>
+        <exclude domain="database" path="deepwave.db"/>
     </cloud-backup>
     <device-transfer>
         <exclude domain="sharedpref" path="deepwave_master_keyset_prefs.xml"/>
         <exclude domain="file" path="datastore/deepwave_credentials.preferences_pb"/>
+        <exclude domain="database" path="deepwave.db"/>
     </device-transfer>
 </data-extraction-rules>