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

cmd/indexexport/main.go

@@ -40,7 +40,7 @@ import (
 // recomputed locally by PopulateLocalCrossReferences after import.
 const catalogColumns = `entity_type, mbid, title, artist_name, artist_mbid,
 	aliases, popularity, listener_count, duration, caa_release_mbid,
-	release_name, primary_type, secondary_types, release_date,
+	release_name, primary_type, secondary_types, release_date, total_tracks,
 	artist_type, country, disambiguation, sort_name, discog_fetched`
 
 var errNoHome = errors.New(
@@ -139,21 +139,27 @@ func run(out string, artists, perArtistRGs, perArtistRecs int) error {
 // the importing client's own trigger rebuilds its FTS on insert.
 func createSchema(db *sql.DB) error {
 	stmts := []string{
+		// Column types mirror the app's own explore_index, because the
+		// export is a straight copy: MBIDs as 16 raw bytes, entity
+		// types as codes.  An importer that meets the older text form
+		// converts it (artifactSelectColumns), so this is a size change
+		// and not a compatibility break.
 		`CREATE TABLE core.explore_index (
-			entity_type      TEXT NOT NULL,
-			mbid             TEXT NOT NULL,
+			entity_type      INTEGER NOT NULL,
+			mbid             BLOB NOT NULL,
 			title            TEXT NOT NULL,
 			artist_name      TEXT NOT NULL,
-			artist_mbid      TEXT NOT NULL,
+			artist_mbid      BLOB NOT NULL,
 			aliases          TEXT NOT NULL DEFAULT '',
 			popularity       INTEGER NOT NULL DEFAULT 0,
 			listener_count   INTEGER NOT NULL DEFAULT 0,
 			duration         INTEGER NOT NULL DEFAULT 0,
-			caa_release_mbid TEXT NOT NULL DEFAULT '',
+			caa_release_mbid BLOB NOT NULL DEFAULT x'',
 			release_name     TEXT NOT NULL DEFAULT '',
 			primary_type     TEXT NOT NULL DEFAULT '',
 			secondary_types  TEXT NOT NULL DEFAULT '',
 			release_date     TEXT NOT NULL DEFAULT '',
+			total_tracks     INTEGER NOT NULL DEFAULT 0,
 			artist_type      TEXT NOT NULL DEFAULT '',
 			country          TEXT NOT NULL DEFAULT '',
 			disambiguation   TEXT NOT NULL DEFAULT '',
@@ -186,7 +192,7 @@ func copyRows(db *sql.DB, artists, perArtistRGs, perArtistRecs int) error {
 	if _, err := db.Exec(`
 		CREATE TEMP TABLE core_artists AS
 		SELECT mbid FROM main.explore_index
-		WHERE entity_type = 'artist'
+		WHERE entity_type = 1 /* artist */
 		ORDER BY popularity DESC
 		LIMIT ?`, artists,
 	); err != nil {
@@ -197,7 +203,7 @@ func copyRows(db *sql.DB, artists, perArtistRGs, perArtistRecs int) error {
 		INSERT INTO core.explore_index (`+catalogColumns+`)
 		SELECT `+catalogColumns+`
 		FROM main.explore_index
-		WHERE entity_type = 'artist'
+		WHERE entity_type = 1 /* artist */
 		  AND mbid IN (SELECT mbid FROM core_artists)`)
 	if err != nil {
 		return err
@@ -205,13 +211,18 @@ func copyRows(db *sql.DB, artists, perArtistRGs, perArtistRecs int) error {
 
 	fmt.Printf("  artists:        %d\n", copied)
 
+	// The entity codes are the catalog's storage form; see
+	// backend/explore/mbid.go.  The exporter copies the local index's
+	// encoding through unchanged, so the artifact carries it too - and
+	// the importer accepts either, so an artifact built before this
+	// still imports.
 	for _, sel := range []struct {
 		label  string
-		entity string
+		entity int
 		limit  int
 	}{
-		{"release groups", "release_group", perArtistRGs},
-		{"recordings", "recording", perArtistRecs},
+		{"release groups", 2 /* release_group */, perArtistRGs},
+		{"recordings", 3 /* recording */, perArtistRecs},
 	} {
 		// The window is over artist_mbid so each artist contributes at
 		// most `limit` rows, ranked by their own listen counts.