feat(database): shape the library like files, and shrink the catalog

Plans 013 and 014, the album page that prompted them, and the smaller
fixes they turned up. Changelog, largest first.

## The local library is shaped like files, not like MusicBrainz

`audio_files` carries its own tags and points at `albums` and
`artists`; `file_genres` is the one real many-to-many. `recordings`,
`release_group_recordings`, `artist_credit`, `artist_credit_artist`,
`recording_genres`, `release_groups` and `release_to_rg` are gone from
the local side, and with them a six-way join in every read, a
`MIN(release_group_id)` subquery in eleven queries and a
first-credited-artist subquery in nine. Measured on a real 25,966-file
library, every many-to-many that model expressed was 1:1 in the data.

- Ownership is a file. `GetFilePathsByRecordingMBIDs`,
  `LibraryMBIDIndex.CheckMBIDs`, `collectLibraryEntities` and
  `pruneStaleLocalCrossReferences` all join `audio_files`, so the 812
  orphaned recordings, 216 release groups and 260 artists that library
  carried are now structurally impossible.
- One projection: every track query selects from the `track_metadata`
  view, one row type, one mapper. Nine hand-rolled copies had drifted
  far enough to report different years on different screens.
- `library_id = 0` means every library, so each list query exists once
  instead of scoped and unscoped with a branch at every call site.
- No migration chain. `sql/schemas/` is the one description of the
  shape; `sql/migrations/`, `applyMigrations` and `schema_migrations`
  are squashed away, along with the drift between them that had sqlc
  generating against a stale schema.
- `database.InsertTestTrack` is the one test seeder; twenty test files
  had been assembling the old FK chain each in its own order.

## The catalog stores its ids as bytes

`explore_index`'s three 36-char MBID columns and its entity-type text
are 16 raw bytes and a small integer. The table and its six indexes go
780 MB to 405 MB on a real 2,052,200-row catalog, which is why a fresh
install is ~0.6 GB rather than ~1.0 GB.

- `backend/explore/mbid.go` is the only place the encoding is known;
  everything above it speaks dashed strings.
- `CHECK(length(mbid) = 16)` makes a stringly write fail at the insert
  rather than silently returning no rows, since SQLite does not coerce
  between TEXT and BLOB.
- The importer asks the artifact what encoding it carries and converts
  on the way in, so the artifact already published keeps working and no
  format bump is needed.
- `indexRowColumns`/`scanIndexRow` replace four copies of a 22-column
  list, and `TestStoredEncodingRoundTrips` sweeps every read path.

## An album page that says how much of the album is yours

- One question, asked once: is there a file. `filePaths` is filled by a
  single batched lookup when the tracklist settles, and the badge, the
  Play count, the dimmed rows and every menu item read it — replacing
  four claims of decreasing confidence that could show a green tick on
  an album whose every action did nothing.
- Play, Play 7 of 12, or no play button at all.
- `total_tracks` on `explore_index` (~2 bytes over 400,677 release
  groups) and on `audio_files` from tags that have always carried it:
  a complete MBID-matched album now makes no catalog call at all, where
  it used to spend the most expensive request the app makes.
- A merged cluster shows the running order the most releases agree on,
  and the version list marks the release you own rather than standing a
  synthetic entry in for it.
- `AlbumReleasesFailed`: a slow fetch is no longer reported as a failed
  one by a 12-second timer.
- Rows not in the library are dimmed in place (with `aria-disabled`)
  instead of the owned ones wearing a green tick and a legend.

## Caches and cover art get ceilings

- Only the three tiers of a cover are stored; the full-resolution copy
  nothing rendered was 1,134 MB of a 1.4 GB covers directory.
- One artist portrait is downloaded and the rest are remembered as
  URLs — 4.1 GB of a 5.3 GB cache was candidates no code path reads.
- `browsedArtBudget` and `httpCacheBudget` bound what an age cannot:
  the same install held art for 5,770 artists in a 1,301-artist
  library.
- `OrphanedArtistImagesJob` joined a bare MBID onto a sharded
  directory, so it deleted the rows that were the only record of the
  files it left behind. `explore.ArtistImageDir` is that layout's one
  definition now.

## The autotag queue asks whether there is work

`tagging_items` was a row per album folder, not a queue, and no query
read the `tag_status` column that held the answer. The four queue
queries ask the files, which matters most where it is least visible:
`startPrefetch` was scoring every album in a tagged library against
MusicBrainz.

## Phantom playlist tracks resolve in place

An M3U8 imported before its files leaves phantom rows; they now match
by path and fall back to position, keep their place in the playlist
when resolved, and pair best-first so two phantoms cannot claim the
same file.

## Playing a track plays the list it is in

Double-click, and Play on a single row's menu, queue the list as
displayed with `startIndex` on that row — the album page and the track
list used to queue one track and discard the album around it. A
multi-row selection still plays exactly itself.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AfVYUVExXsx1nSWrXN8mAh

backend/database/database_test.go

@@ -312,31 +312,13 @@ func TestPhantomPlaylistTracksAreCleaned(t *testing.T) {
 
 	// Create prerequisite data: artist_credit, recording,
 	// audio_file.
-	_, err := db.ExecContext(
-		"INSERT INTO artist_credit (id, text) VALUES (1, 'Test Artist')",
-	)
-	if err != nil {
-		t.Fatalf("insert artist_credit: %v", err)
-	}
-
-	_, err = db.ExecContext(
-		"INSERT INTO recordings (id, name, artist_credit_id) " +
-			"VALUES (1, 'Test Song', 1)",
-	)
-	if err != nil {
-		t.Fatalf("insert recording: %v", err)
-	}
-
-	_, err = db.ExecContext(
-		"INSERT INTO audio_files "+
-			"(id, file_path, length_milliseconds, file_type_id, "+
-			"recording_id, library_id) "+
-			"VALUES (1, '/test/music/song.mp3', 180000, 0, 1, ?)",
-		libID,
-	)
-	if err != nil {
-		t.Fatalf("insert audio_file: %v", err)
-	}
+	InsertTestTrack(t, db, TestTrack{
+		FilePath:  "/test/music/song.mp3",
+		Title:     "Test Song",
+		Artist:    "Test Artist",
+		LengthMs:  180000,
+		LibraryID: libID,
+	})
 
 	// Create playlist.
 	playlist, err := db.Queries.CreatePlaylist(
@@ -442,39 +424,18 @@ func TestAudioFilesLibraryForeignKey(t *testing.T) {
 	db, libID := NewTestDBWithLibrary(t, "Test", "/test/fk-lib")
 
 	// Insert prerequisite recording.
+	InsertTestTrack(t, db, TestTrack{
+		FilePath:  "/test/track.mp3",
+		Title:     "Track",
+		Artist:    "Test",
+		LibraryID: libID,
+	})
+
+	// Insert audio file with invalid library_id - should fail FK.
 	_, err := db.ExecContext(
-		"INSERT INTO artist_credit (id, text) VALUES (1, 'Test')",
-	)
-	if err != nil {
-		t.Fatalf("insert artist_credit: %v", err)
-	}
-
-	_, err = db.ExecContext(
-		"INSERT INTO recordings (id, name, artist_credit_id) " +
-			"VALUES (1, 'Track', 1)",
-	)
-	if err != nil {
-		t.Fatalf("insert recording: %v", err)
-	}
-
-	// Insert audio file with valid library_id — should succeed.
-	_, err = db.ExecContext(
-		"INSERT INTO audio_files "+
-			"(id, file_path, length_milliseconds, file_type_id, "+
-			"recording_id, library_id) "+
-			"VALUES (1, '/test/song.mp3', 180000, 0, 1, ?)",
-		libID,
-	)
-	if err != nil {
-		t.Fatalf("insert audio_file with valid library: %v", err)
-	}
-
-	// Insert audio file with invalid library_id — should fail FK.
-	_, err = db.ExecContext(
 		"INSERT INTO audio_files " +
-			"(id, file_path, length_milliseconds, file_type_id, " +
-			"recording_id, library_id) " +
-			"VALUES (2, '/test/song2.mp3', 200000, 0, 1, 999)",
+			"(id, file_path, length_milliseconds, file_type_id, library_id) " +
+			"VALUES (2, '/test/song2.mp3', 200000, 0, 999)",
 	)
 	if err == nil {
 		t.Error(
@@ -483,16 +444,16 @@ func TestAudioFilesLibraryForeignKey(t *testing.T) {
 	}
 
 	// Count files by library.
-	count, err := db.Queries.CountAudioFilesByLibrary(
+	count, err := db.Queries.CountAudioFiles(
 		db.Ctx, libID,
 	)
 	if err != nil {
-		t.Fatalf("CountAudioFilesByLibrary: %v", err)
+		t.Fatalf("CountAudioFiles: %v", err)
 	}
 
 	if count != 1 {
 		t.Errorf(
-			"CountAudioFilesByLibrary = %d, want 1", count,
+			"CountAudioFiles = %d, want 1", count,
 		)
 	}
 }
@@ -503,31 +464,13 @@ func TestTrackMetadataViewHasLibraryID(t *testing.T) {
 	db, libID := NewTestDBWithLibrary(t, "Test", "/test/view-lib")
 
 	// Insert prerequisites.
-	_, err := db.ExecContext(
-		"INSERT INTO artist_credit (id, text) VALUES (1, 'View Artist')",
-	)
-	if err != nil {
-		t.Fatalf("insert artist_credit: %v", err)
-	}
-
-	_, err = db.ExecContext(
-		"INSERT INTO recordings (id, name, artist_credit_id) " +
-			"VALUES (1, 'View Track', 1)",
-	)
-	if err != nil {
-		t.Fatalf("insert recording: %v", err)
-	}
-
-	_, err = db.ExecContext(
-		"INSERT INTO audio_files "+
-			"(id, file_path, length_milliseconds, file_type_id, "+
-			"recording_id, library_id) "+
-			"VALUES (1, '/test/view.mp3', 200000, 0, 1, ?)",
-		libID,
-	)
-	if err != nil {
-		t.Fatalf("insert audio_file: %v", err)
-	}
+	InsertTestTrack(t, db, TestTrack{
+		FilePath:  "/test/view.mp3",
+		Title:     "View Track",
+		Artist:    "View Artist",
+		LengthMs:  200000,
+		LibraryID: libID,
+	})
 
 	// Query track_metadata VIEW and verify library_id is present
 	// with the correct value.
@@ -842,29 +785,13 @@ func TestPlayHistoryTable(t *testing.T) {
 
 	// Round-trip: insert a play_history row and verify play_count update.
 	// First, set up test data. The test DB already has library id=0.
-	_, err = db.ExecContext(
-		"INSERT OR IGNORE INTO artist_credit (id, text) VALUES (1, 'Test Artist')",
-	)
-	if err != nil {
-		t.Fatalf("insert artist_credit: %v", err)
-	}
-
-	_, err = db.ExecContext(
-		`INSERT OR IGNORE INTO recordings (id, name, artist_credit_id, track_number, disc_number)
-		 VALUES (1, 'Test Track', 1, 1, 1)`,
-	)
-	if err != nil {
-		t.Fatalf("insert recording: %v", err)
-	}
-
-	_, err = db.ExecContext(
-		`INSERT INTO audio_files
-		 (id, file_path, length_milliseconds, file_type_id, recording_id, library_id)
-		 VALUES (1, '/test/track.mp3', 180000, 0, 1, 0)`,
-	)
-	if err != nil {
-		t.Fatalf("insert audio_file: %v", err)
-	}
+	InsertTestTrack(t, db, TestTrack{
+		FilePath:    "/test/play_history.mp3",
+		Title:       "Test Track",
+		Artist:      "Test Artist",
+		TrackNumber: 1,
+		DiscNumber:  1,
+	})
 
 	// Verify default play_count is 0.
 	var playCount int64