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/explore/artifactimport_test.go

@@ -202,7 +202,7 @@ func TestImportCoreArtifactPreservesLocalData(t *testing.T) {
 
 	if err := db.QueryRowWriter(`
 		SELECT popularity, duration, in_library, discog_fetched
-		FROM explore_index WHERE mbid = ?`, recA,
+		FROM explore_index WHERE mbid = ?`, dbMBID(recA),
 	).Scan(&popularity, &duration, &inLibrary, &discogFetched); err != nil {
 		t.Fatalf("read merged row: %v", err)
 	}
@@ -376,7 +376,7 @@ func TestAddFromCacheNeverStoresMBIDAsName(t *testing.T) {
 
 	var artistName string
 	if err := db.QueryRowWriter(
-		`SELECT artist_name FROM explore_index WHERE mbid = ?`, rgA,
+		`SELECT artist_name FROM explore_index WHERE mbid = ?`, dbMBID(rgA),
 	).Scan(&artistName); err != nil {
 		t.Fatalf("read release group: %v", err)
 	}
@@ -391,7 +391,7 @@ func TestAddFromCacheNeverStoresMBIDAsName(t *testing.T) {
 	})
 
 	if err := db.QueryRowWriter(
-		`SELECT artist_name FROM explore_index WHERE mbid = ?`, rgA,
+		`SELECT artist_name FROM explore_index WHERE mbid = ?`, dbMBID(rgA),
 	).Scan(&artistName); err != nil {
 		t.Fatalf("re-read release group: %v", err)
 	}
@@ -442,3 +442,158 @@ func TestArtifactColumnsMatchExporter(t *testing.T) {
 			exporter, importer)
 	}
 }
+
+// TestImportCoreArtifactAcceptsBothEncodings is the compatibility half
+// of the storage change.
+//
+// The catalog stores an MBID as 16 raw bytes and an entity type as a
+// code, which took the table and its indexes from 677 MB to 389 MB. A
+// published artifact carries whichever form the exporter that built it
+// used, and there is one already out there in the older text form — so
+// the importer decides by asking the artifact, not by trusting a
+// version number, and both must land identically.
+func TestImportCoreArtifactAcceptsBothEncodings(t *testing.T) {
+	compact := filepath.Join(t.TempDir(), "core-index.db")
+
+	db, err := sql.Open("sqlite", "file:"+compact)
+	if err != nil {
+		t.Fatalf("open artifact: %v", err)
+	}
+
+	if _, err := db.Exec(`CREATE TABLE explore_index (
+		entity_type      INTEGER NOT NULL,
+		mbid             BLOB NOT NULL,
+		title            TEXT NOT NULL,
+		artist_name      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 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 '',
+		artist_type      TEXT NOT NULL DEFAULT '',
+		country          TEXT NOT NULL DEFAULT '',
+		disambiguation   TEXT NOT NULL DEFAULT '',
+		sort_name        TEXT NOT NULL DEFAULT '',
+		discog_fetched   INTEGER NOT NULL DEFAULT 0,
+		PRIMARY KEY (mbid)
+	)`); err != nil {
+		t.Fatalf("create artifact table: %v", err)
+	}
+
+	if _, err := db.Exec(
+		`CREATE TABLE artifact_meta (key TEXT PRIMARY KEY, value TEXT NOT NULL)`,
+	); err != nil {
+		t.Fatalf("create artifact meta: %v", err)
+	}
+
+	for k, v := range validMeta() {
+		if _, err := db.Exec(
+			"INSERT INTO artifact_meta (key, value) VALUES (?, ?)", k, v,
+		); err != nil {
+			t.Fatalf("write artifact meta: %v", err)
+		}
+	}
+
+	if _, err := db.Exec(`
+		INSERT INTO explore_index (entity_type, mbid, title, artist_name, artist_mbid, popularity)
+		VALUES (1, ?, 'Artist A', 'Artist A', ?, 5000)`,
+		mbidBytes(artA), mbidBytes(artA),
+	); err != nil {
+		t.Fatalf("write artifact row: %v", err)
+	}
+
+	_ = db.Close()
+
+	live := database.NewTestDB(t)
+	si := NewSearchIndex(live, nil, nil, testLogger())
+
+	if err := si.importCoreArtifact(context.Background(), compact); err != nil {
+		t.Fatalf("importCoreArtifact (compact): %v", err)
+	}
+
+	got := si.LookupArtistByMBID(artA)
+	if got == nil {
+		t.Fatal("artist from a compact artifact was not imported")
+	}
+
+	if got.Title != "Artist A" || got.MBID != artA {
+		t.Errorf("imported %+v, want Artist A / %s", got, artA)
+	}
+}
+
+// TestImportCoreArtifactReadsTotalsWhenPresent covers both halves of the
+// denominator's arrival: an artifact that carries total_tracks imports
+// it, and one built before the column existed still imports at all.
+//
+// The second half is the one worth a test.  Adding a column to the
+// importer's SELECT list is how you break every artifact already
+// published - "no such column: total_tracks", on a file nobody can
+// re-cut retroactively - so the importer asks the artifact what it has,
+// the same way it asks which encoding it uses.
+func TestImportCoreArtifactReadsTotalsWhenPresent(t *testing.T) {
+	path := writeTestArtifact(t, validMeta(), []artifactRow{
+		{"release_group", rgA, "Big Album", "Solo Star", artA, 5000},
+	})
+
+	// The exporter writes the column; writeTestArtifact builds the older
+	// shape, so add it here rather than changing every other test's
+	// fixture to carry a value they do not use.
+	artifact, err := sql.Open("sqlite", "file:"+path)
+	if err != nil {
+		t.Fatalf("reopen artifact: %v", err)
+	}
+
+	for _, stmt := range []string{
+		`ALTER TABLE explore_index ADD COLUMN total_tracks INTEGER NOT NULL DEFAULT 0`,
+		`UPDATE explore_index SET total_tracks = 12`,
+	} {
+		if _, err := artifact.Exec(stmt); err != nil {
+			t.Fatalf("add total_tracks: %v", err)
+		}
+	}
+
+	_ = artifact.Close()
+
+	live := database.NewTestDB(t)
+	si := NewSearchIndex(live, nil, nil, testLogger())
+
+	if err := si.importCoreArtifact(context.Background(), path); err != nil {
+		t.Fatalf("importCoreArtifact: %v", err)
+	}
+
+	rg := si.LookupReleaseGroupByMBID(rgA)
+	if rg == nil {
+		t.Fatal("release group was not imported")
+	}
+
+	if rg.TotalTracks != 12 {
+		t.Errorf("TotalTracks = %d, want 12", rg.TotalTracks)
+	}
+
+	// And the shape that predates the column: the same import, from an
+	// artifact that has no total_tracks at all.
+	older := writeTestArtifact(t, validMeta(), []artifactRow{
+		{"release_group", rgB, "Duet Album", "Solo Star", artA, 4000},
+	})
+
+	live2 := database.NewTestDB(t)
+	si2 := NewSearchIndex(live2, nil, nil, testLogger())
+
+	if err := si2.importCoreArtifact(context.Background(), older); err != nil {
+		t.Fatalf("importCoreArtifact (no total_tracks column): %v", err)
+	}
+
+	old := si2.LookupReleaseGroupByMBID(rgB)
+	if old == nil {
+		t.Fatal("release group from a column-less artifact was not imported")
+	}
+
+	if old.TotalTracks != 0 {
+		t.Errorf("TotalTracks = %d, want 0 (the catalog does not say)", old.TotalTracks)
+	}
+}