add the Downloaded filter to the library tabs

One toggle per tab, persisted with the rest of the list query, narrowing to
entities that have at least one completed download. It rides the existing filter
SQL: every album, artist and playlist paging query takes a flag and the shared
filter constant adds an EXISTS over song_downloads, so it composes with the
sort, search and starred filter rather than being a separate mode.

The filters sheet now renders on every tab, since playlists support Downloaded
but not Starred.

app/src/test/kotlin/com/subtracks/data/db/LibraryDaoTest.kt

@@ -9,8 +9,11 @@ import androidx.test.core.app.ApplicationProvider
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import com.subtracks.data.model.Album
 import com.subtracks.data.model.Artist
+import com.subtracks.data.model.DownloadStatus
 import com.subtracks.data.model.Playlist
+import com.subtracks.data.model.PlaylistSong
 import com.subtracks.data.model.Song
+import com.subtracks.data.model.SongDownload
 import com.subtracks.data.model.Source
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.test.runTest
@@ -290,6 +293,53 @@ class LibraryDaoTest {
             assertTrue(plan, plan.contains("TEMP B-TREE"))
         }
 
+    @Test
+    fun theDownloadedFilterKeepsOnlyEntitiesWithACompletedDownload() =
+        runTest {
+            val sourceId = source()
+            val dao = db.libraryDao()
+            dao.upsertAlbums(
+                listOf(
+                    album(sourceId, "al-1", "Downloaded", year = 2000, starred = null),
+                    album(sourceId, "al-2", "Empty", year = 2001, starred = null),
+                ),
+            )
+            dao.upsertArtists(listOf(artist(sourceId, "ar-1", "Artist", albumCount = 2)))
+            dao.upsertSongs(
+                listOf(
+                    song(sourceId, "s1", "One", starred = null),
+                    song(sourceId, "s2", "Two", starred = null).copy(albumId = "al-2"),
+                ),
+            )
+            dao.upsertPlaylists(
+                listOf(
+                    playlist(sourceId, "pl-1", "Has download", created = 0, changed = 0),
+                    playlist(sourceId, "pl-2", "No download", created = 1, changed = 1),
+                ),
+            )
+            dao.upsertPlaylistSongs(
+                listOf(
+                    PlaylistSong(sourceId, "pl-1", "s1", 0),
+                    PlaylistSong(sourceId, "pl-2", "s2", 0),
+                ),
+            )
+            db.downloadDao().upsert(SongDownload(sourceId, "s1", DownloadStatus.Completed))
+
+            assertEquals(
+                listOf("Downloaded"),
+                dao.albumsByName(sourceId, 0, "", downloadedFilter = 1).page().map { it.name },
+            )
+            assertEquals(
+                listOf("ar-1"),
+                dao.artistsByName(sourceId, 0, "", downloadedFilter = 1).page().map { it.id },
+            )
+            assertEquals(
+                listOf("pl-1"),
+                dao.playlistsByName(sourceId, "", downloadedFilter = 1).page().map { it.id },
+            )
+            assertEquals(2, dao.albumsByName(sourceId, 0, "").page().size)
+        }
+
     private suspend fun plan(sql: String): String =
         db.useReaderConnection { connection ->
             connection.usePrepared("EXPLAIN QUERY PLAN $sql") { statement ->