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/library/removal_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 
 	"yellowjacket/backend/coverart"
+	"yellowjacket/backend/database"
 	"yellowjacket/backend/database/sql/sqlcgen"
 )
 
@@ -30,19 +31,6 @@ func seedRemovableLibrary(
 		t.Fatalf("create library: %v", err)
 	}
 
-	ac, err := q.UpsertArtistCredit(ctx, "Test Artist")
-	if err != nil {
-		t.Fatalf("upsert artist credit: %v", err)
-	}
-
-	rec, err := q.CreateRecordingFull(ctx, sqlcgen.CreateRecordingFullParams{
-		Name:           "Test Song",
-		ArtistCreditID: ac.ID,
-	})
-	if err != nil {
-		t.Fatalf("create recording: %v", err)
-	}
-
 	if _, err := lib.db.ExecContext(
 		`INSERT INTO cover_art (is_embedded, file_path, mime_type)
 		 VALUES (0, ?, 'image/jpeg')`, coverPath,
@@ -50,15 +38,14 @@ func seedRemovableLibrary(
 		t.Fatalf("insert cover art: %v", err)
 	}
 
-	if _, err := q.CreateAudioFile(ctx, sqlcgen.CreateAudioFileParams{
-		FilePath:           "/music/song.mp3",
-		LengthMilliseconds: 180000,
-		RecordingID:        rec.ID,
-		LibraryID:          library.ID,
-		Basename:           "song.mp3",
-	}); err != nil {
-		t.Fatalf("create audio file: %v", err)
-	}
+	database.InsertTestTrack(t, lib.db, database.TestTrack{
+		FilePath:  "/music/song.mp3",
+		Title:     "Test Song",
+		Artist:    "Test Artist",
+		Album:     "Test Album",
+		LengthMs:  180000,
+		LibraryID: library.ID,
+	})
 
 	// Every scanned library gets tagging_items rows, one per album
 	// folder.  These FK-reference libraries.
@@ -137,9 +124,9 @@ func TestRemoveLibrary_WithTaggingItems(t *testing.T) {
 
 	for _, table := range []string{
 		"audio_files",
-		"recordings",
-		"artist_credit",
+		"albums",
 		"artists",
+		"file_genres",
 		"tagging_items",
 		"tagging_candidates",
 		"cover_art",
@@ -158,18 +145,16 @@ func TestRemoveLibrary_DeletesCoverArtVariants(t *testing.T) {
 	lib, _ := setupTestLibrary(t)
 
 	dir := t.TempDir()
-	original := filepath.Join(dir, "abc123.jpg")
 
-	paths := []string{original}
+	var paths []string
 	for _, tier := range thumbnailTiers {
 		paths = append(paths, filepath.Join(
 			dir, coverart.SizedFilename("abc123.jpg", tier.Suffix),
 		))
 	}
 
-	paths = append(paths, filepath.Join(
-		dir, coverart.SizedFilename("abc123.jpg", legacyThumbSuffix),
-	))
+	// The largest tier is what cover_art.file_path names.
+	cover := filepath.Join(dir, coverart.SizedFilename("abc123.jpg", "_lg"))
 
 	for _, p := range paths {
 		if err := os.WriteFile(p, []byte("img"), 0o600); err != nil {
@@ -177,7 +162,7 @@ func TestRemoveLibrary_DeletesCoverArtVariants(t *testing.T) {
 		}
 	}
 
-	library := seedRemovableLibrary(t, lib, original)
+	library := seedRemovableLibrary(t, lib, cover)
 
 	if _, err := lib.RemoveLibrary(library.ID); err != nil {
 		t.Fatalf("RemoveLibrary: %v", err)
@@ -190,19 +175,17 @@ func TestRemoveLibrary_DeletesCoverArtVariants(t *testing.T) {
 	}
 }
 
-// CoverArtFileSet must cover the original, every generated tier, and
-// the legacy _thumb name.
+// CoverArtFileSet must cover every generated tier, from any of them:
+// cover_art.file_path names the largest, and the others are derived.
 func TestCoverArtFileSet(t *testing.T) {
 	t.Parallel()
 
-	got := CoverArtFileSet("/covers/abc123.jpg")
+	got := CoverArtFileSet("/covers/abc123_lg.jpg")
 
 	want := []string{
-		"/covers/abc123.jpg",
 		"/covers/abc123_sm.jpg",
 		"/covers/abc123_md.jpg",
 		"/covers/abc123_lg.jpg",
-		"/covers/abc123_thumb.jpg",
 	}
 
 	if len(got) != len(want) {