address review: localize connection errors, tighten i18n guard, drop dead resources

- AddSourceViewModel resolves SubsonicException.uiMessage too, so malformed/
  HTTP/truncated responses show localized text instead of the raw parser
  message; add a regression test.
- StringResourcesTest now requires an 'other' quantity in every plural and
  asserts exact placeholder (index and conversion) equality, both of which
  could previously pass while crashing getQuantityString at runtime.
- Map the pre-enum song_downloads.error sentences back to their DownloadError
  so existing failed rows keep their specific message.
- Localize the media-session star/unstar button label.
- Remove 12 unreferenced resources (queue name, filter year, sync_failed, and
  the unused codec_* strings; codec labels stay in AudioEncoding).
- Make buildTree's fallback arguments required; only tests used the defaults.

app/src/main/kotlin/com/subtracks/data/model/Download.kt

@@ -130,5 +130,25 @@ class DownloadErrorConverter {
     fun fromDownloadError(error: DownloadError): String = error.name
 
     @ColumnTypeConverter
-    fun toDownloadError(value: String): DownloadError = DownloadError.entries.firstOrNull { it.name == value } ?: DownloadError.Failed
+    fun toDownloadError(value: String): DownloadError =
+        DownloadError.entries.firstOrNull { it.name == value }
+            ?: LEGACY_DOWNLOAD_ERRORS[value]
+            ?: DownloadError.Failed
 }
+
+private val LEGACY_DOWNLOAD_ERRORS =
+    mapOf(
+        "Not enough space to download" to DownloadError.NoSpace,
+        "Storage is unavailable" to DownloadError.StorageUnavailable,
+        "Could not write the download" to DownloadError.WriteFailed,
+        "The server refused to send this track" to DownloadError.ServerRefused,
+        "The server redirected too many times" to DownloadError.TooManyRedirects,
+        "The download could not be resumed" to DownloadError.ResumeFailed,
+        "Download failed" to DownloadError.Failed,
+        "The downloaded file is missing" to DownloadError.FileMissing,
+        "The server sent an error instead of the track" to DownloadError.ServerError,
+        "Can't download: the server address is unavailable" to DownloadError.NoAddress,
+        "Nothing left to download from this list" to DownloadError.NothingLeft,
+        "The download stopped unexpectedly" to DownloadError.Stopped,
+        "Can't download from a source that isn't active" to DownloadError.InactiveSource,
+    )

app/src/main/kotlin/com/subtracks/data/sync/SyncManager.kt

@@ -2,7 +2,6 @@ package com.subtracks.data.sync
 
 import android.util.Log
 import com.subtracks.R
-import com.subtracks.UiException
 import com.subtracks.UiMessage
 import com.subtracks.data.db.SubtracksDatabase
 import com.subtracks.data.repo.QueueRepository
@@ -73,10 +72,6 @@ class SyncManager(
                             UiMessage(R.string.error_no_server)
                         }
 
-                        is UiException -> {
-                            failure.uiMessage
-                        }
-
                         else -> {
                             (failure as? SubsonicException)?.uiMessage
                                 ?: UiMessage(R.string.sync_failed_detail, listOf(failure.message ?: ""))

app/src/main/kotlin/com/subtracks/playback/PlaybackService.kt

@@ -28,6 +28,7 @@ import coil3.SingletonImageLoader
 import com.google.common.util.concurrent.Futures
 import com.google.common.util.concurrent.ListenableFuture
 import com.subtracks.MainActivity
+import com.subtracks.R
 import com.subtracks.data.repo.LibraryRepository
 import com.subtracks.data.repo.SourceRepository
 import com.subtracks.data.source.StarType
@@ -176,7 +177,7 @@ class PlaybackService : MediaSessionService() {
         CommandButton
             .Builder(if (isStarred) CommandButton.ICON_STAR_FILLED else CommandButton.ICON_STAR_UNFILLED)
             .setSessionCommand(STAR_COMMAND)
-            .setDisplayName(if (isStarred) "Unstar" else "Star")
+            .setDisplayName(getString(if (isStarred) R.string.actions_unstar else R.string.actions_star))
             .build()
 
     private fun streamingClient(): OkHttpClient =

app/src/main/kotlin/com/subtracks/ui/downloads/DownloadsViewModel.kt

@@ -93,8 +93,8 @@ class DownloadsViewModel(
 
 internal fun buildTree(
     songs: List<DownloadedSong>,
-    unknownArtist: String = "Unknown artist",
-    unknownAlbum: String = "Unknown album",
+    unknownArtist: String,
+    unknownAlbum: String,
 ): DownloadTree =
     DownloadTree(
         artists =

app/src/main/kotlin/com/subtracks/ui/settings/AddSourceViewModel.kt

@@ -7,6 +7,7 @@ import com.subtracks.R
 import com.subtracks.UiException
 import com.subtracks.data.repo.DownloadRepository
 import com.subtracks.data.repo.SourceRepository
+import com.subtracks.data.source.subsonic.SubsonicException
 import com.subtracks.data.sync.SyncManager
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
@@ -101,8 +102,8 @@ class AddSourceViewModel(
                                 }
                             },
                             { error ->
-                                (error as? UiException)?.uiMessage?.resolve(resources)
-                                    ?: resources.getString(R.string.connection_failed, error.message)
+                                val ui = (error as? UiException)?.uiMessage ?: (error as? SubsonicException)?.uiMessage
+                                ui?.resolve(resources) ?: resources.getString(R.string.connection_failed, error.message)
                             },
                         ),
                     isError = result.isFailure,