address the bulk download review

- Cancelling a list while its download loop was still enqueueing missed every
  song queued after the cancel looked. The loop now holds the lock for the whole
  queue, so a cancel waits for it to finish and then removes all of it. That
  needed the enqueue helper split into a locked entry point and a body the loop
  can call while already holding the lock — calling the locked one from inside
  the lock deadlocked, which is what hung the tests.
- An empty resolved list now says so instead of doing nothing.
- One song failing to enqueue no longer aborts the rest of the batch.
- The artist actions resolve through the albums the artist page lists, matching
  what is on screen, rather than through songs.artistId, which for a guest on a
  compilation enqueued nothing.
- Bulk actions are one `applyAction` on the repository, so the three view models
  and both screens stop repeating the same dispatch.
- Tests: the playlist and artist resolve paths, a Running row counted as
  downloading, the action dispatch, and the action rule moved to a plain unit
  test.

app/src/main/kotlin/com/subtracks/ui/library/AlbumDetailViewModel.kt

@@ -3,6 +3,7 @@ package com.subtracks.ui.library
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.subtracks.data.model.Album
+import com.subtracks.data.model.BulkDownloadAction
 import com.subtracks.data.model.CoverArtRef
 import com.subtracks.data.model.Disc
 import com.subtracks.data.model.DownloadList
@@ -46,18 +47,10 @@ class AlbumDetailViewModel(
             .flatMapLatest { downloadRepository.status(it, DownloadList.Album, albumId) }
             .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), ListDownloadStatus())
 
-    fun downloadAll() {
-        viewModelScope.launch { downloadRepository.downloadAll(sourceId.first(), DownloadList.Album, albumId) }
-    }
-
-    fun cancelDownloads() {
-        viewModelScope.launch { downloadRepository.cancelAll(sourceId.first(), DownloadList.Album, albumId) }
-    }
-
-    fun deleteDownloads() {
+    fun onDownloadAction(action: BulkDownloadAction) {
         viewModelScope.launch {
-            downloadRepository.deleteAll(sourceId.first(), DownloadList.Album, albumId)
-            playbackController.refreshMediaItems()
+            downloadRepository.applyAction(sourceId.first(), DownloadList.Album, albumId, action)
+            if (action == BulkDownloadAction.Delete) playbackController.refreshMediaItems()
         }
     }