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/home/home.go

@@ -101,7 +101,7 @@ const (
 // purpose: the home page needs one list of albums, not the library
 // package.
 type Library interface {
-	GetAllAlbums() ([]library.Album, error)
+	GetAlbums(libraryID int64) ([]library.Album, error)
 }
 
 // Service builds the home page's shelves.
@@ -132,7 +132,7 @@ func (s *Service) GetShelves() ([]Shelf, error) {
 		ctx = context.Background()
 	}
 
-	albums, err := s.lib.GetAllAlbums()
+	albums, err := s.lib.GetAlbums(0)
 	if err != nil {
 		return nil, err
 	}

backend/home/home_test.go

@@ -17,7 +17,7 @@ type fakeLibrary struct {
 	err    error
 }
 
-func (f fakeLibrary) GetAllAlbums() ([]library.Album, error) {
+func (f fakeLibrary) GetAlbums(int64) ([]library.Album, error) {
 	return f.albums, f.err
 }
 
@@ -34,46 +34,32 @@ func seed(
 ) int64 {
 	t.Helper()
 
-	exec := func(query string, args ...any) {
-		t.Helper()
-
-		if _, err := db.ExecContext(query, args...); err != nil {
-			t.Fatalf("seed %q: %v", query, err)
-		}
+	var genres []string
+	if genre != "" {
+		genres = []string{genre}
 	}
 
-	exec(`INSERT INTO artist_credit (text) VALUES (?)
-	      ON CONFLICT DO NOTHING`, artist)
-	exec(`INSERT INTO release_groups (name, album_artist_credit_id)
-	      VALUES (?, (SELECT id FROM artist_credit WHERE text = ?))`,
-		name, artist)
-	exec(`INSERT INTO recordings (name, artist_credit_id)
-	      VALUES (?, (SELECT id FROM artist_credit WHERE text = ?))`,
-		name+" track", artist)
-	exec(`INSERT INTO release_group_recordings (release_group_id, recording_id)
-	      VALUES ((SELECT MAX(id) FROM release_groups),
-	              (SELECT MAX(id) FROM recordings))`)
-	exec(`INSERT INTO file_types (extension) VALUES ('mp3')
-	      ON CONFLICT DO NOTHING`)
-	exec(`INSERT INTO audio_files
-	        (file_path, length_milliseconds, file_type_id, recording_id,
-	         play_count, last_played)
-	      VALUES (?, 1000,
-	              (SELECT MAX(id) FROM file_types),
-	              (SELECT MAX(id) FROM recordings),
-	              ?, ?)`,
-		"/music/"+name+".mp3", playCount, nullable(lastPlayed))
+	fileID := database.InsertTestTrack(t, db, database.TestTrack{
+		FilePath:  "/music/" + name + ".mp3",
+		Title:     name + " track",
+		Artist:    artist,
+		Album:     name,
+		Genres:    genres,
+		LengthMs:  1000,
+		PlayCount: int64(playCount),
+	})
 
-	if genre != "" {
-		exec(`INSERT INTO genres (name) VALUES (?) ON CONFLICT DO NOTHING`, genre)
-		exec(`INSERT INTO recording_genres (recording_id, genre_id)
-		      VALUES ((SELECT MAX(id) FROM recordings),
-		              (SELECT id FROM genres WHERE name = ?))`, genre)
+	if lastPlayed != "" {
+		if _, err := db.ExecContext(
+			"UPDATE audio_files SET last_played = ? WHERE id = ?", lastPlayed, fileID,
+		); err != nil {
+			t.Fatalf("seed last_played: %v", err)
+		}
 	}
 
 	var id int64
 	if err := db.QueryRowWriter(
-		`SELECT MAX(id) FROM release_groups`,
+		"SELECT album_id FROM audio_files WHERE id = ?", fileID,
 	).Scan(&id); err != nil {
 		t.Fatalf("seed: read album id: %v", err)
 	}
@@ -81,14 +67,6 @@ func seed(
 	return id
 }
 
-func nullable(s string) any {
-	if s == "" {
-		return nil
-	}
-
-	return s
-}
-
 func shelfKinds(shelves []home.Shelf) []home.Kind {
 	kinds := make([]home.Kind, 0, len(shelves))
 	for _, s := range shelves {