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/datamap/datamap.go

@@ -105,13 +105,10 @@ var internalTables = map[string]bool{
 // tables is the catalog.  Keep it alphabetical.
 var tables = []Table{
 	{
-		Name: "artist_credit", Kind: Owned, Lifetime: Swept,
-		Note: "Credit strings parsed from file tags. Orphan-swept when " +
-			"no recording references them.",
-	},
-	{
-		Name: "artist_credit_artist", Kind: Owned, Lifetime: Swept,
-		Note: "Join table between credits and artists.",
+		Name: "albums", Kind: Owned, Lifetime: Swept,
+		Note: "Albums as named by file tags — the local counterpart of a " +
+			"catalog release group, which is a different thing and lives " +
+			"in explore_index. Swept when the last file on one goes.",
 	},
 	{
 		Name: "artist_enrichment", Kind: Derived, Lifetime: Retained,
@@ -138,11 +135,12 @@ var tables = []Table{
 	},
 	{
 		Name: "audio_files", Kind: Owned, Lifetime: Swept,
-		Note: "MIXED KIND. Mostly an owned projection of files on disk, " +
-			"but play_count, last_played and tag_status are authored and " +
-			"exist nowhere else. Deleting a row to rebuild it destroys " +
-			"that authored state — which is why a file rename currently " +
-			"loses play counts. See the data architecture plan.",
+		Note: "MIXED KIND. One row per file, carrying its tags: mostly an " +
+			"owned projection of what is on disk, but play_count, " +
+			"last_played and tag_status are authored and exist nowhere " +
+			"else. Deleting a row to rebuild it destroys that authored " +
+			"state — which is why a file rename currently loses play " +
+			"counts. See the data architecture plan.",
 	},
 	{
 		Name: "cover_art", Kind: Owned, Lifetime: Swept,
@@ -209,6 +207,15 @@ var tables = []Table{
 			"rescan clears it \u2014 the only way back for a path removed by " +
 			"mistake.",
 	},
+	{
+		Name: "file_genres", Kind: Owned, Lifetime: Swept,
+		Note: "Genres per file. The one many-to-many in the local library " +
+			"that really is one. It cascades with the *file*, but the " +
+			"genre_id key is NO ACTION, so a genre cannot be deleted " +
+			"while a link survives — the genre sweep runs after the file " +
+			"sweep for that reason, and only deletes genres nothing " +
+			"references.",
+	},
 	{
 		Name: "file_types", Kind: Derived, Lifetime: Retained,
 		Note: "Static lookup rows seeded from code, not user data.",
@@ -232,6 +239,15 @@ var tables = []Table{
 		Note: "The directories the user chose. Removed only by explicit " +
 			"user action via RemoveLibrary.",
 	},
+	{
+		Name: "lyrics", Kind: Cache, Lifetime: Cascade,
+		Note: "MIXED KIND, and it says which: source='tag' is Owned (any " +
+			"rescan reads it back off the file) and source='lrclib' is " +
+			"Cache (re-fetching it is network traffic and someone else's " +
+			"rate limit). These used to be one untyped column on " +
+			"recordings, in a table classified Owned, so 24,294 rows in a " +
+			"real library could not say which of the two they were.",
+	},
 	{
 		Name: "lyrics_index", Kind: Derived, Lifetime: Retained, FTS: true,
 		Note: "Full-text index over embedded and fetched lyrics. Rebuilt " +
@@ -266,32 +282,11 @@ var tables = []Table{
 		Note: "Queue entries. Cascade with their track; the queue is " +
 			"compacted afterwards.",
 	},
-	{
-		Name: "recording_genres", Kind: Owned, Lifetime: Swept,
-		Note: "Join table between recordings and genres.",
-	},
-	{
-		Name: "recordings", Kind: Owned, Lifetime: Swept,
-		Note: "Tracks as parsed from file tags. Orphan-swept.",
-	},
-	{
-		Name: "release_group_recordings", Kind: Owned, Lifetime: Swept,
-		Note: "Join table between release groups and recordings.",
-	},
-	{
-		Name: "release_groups", Kind: Owned, Lifetime: Swept,
-		Note: "Albums as parsed from file tags. Orphan-swept.",
-	},
 	{
 		Name: "release_to_rg", Kind: Cache, Lifetime: Retained,
-		Note: "Release to release-group mapping from the dump.",
-	},
-	{
-		Name: "schema_migrations", Kind: Derived, Lifetime: Retained,
-		Note: "Bookkeeping for sql/migrations: which numbered files have " +
-			"run. Safe to lose — replaying an already-applied migration " +
-			"tolerates its ALTER TABLE ADD COLUMN as a no-op and just " +
-			"re-records it.",
+		Note: "Release to release-group mapping, captured during a local " +
+			"dump import and read by the incremental listen-count " +
+			"refresh. Empty unless this install built its own index.",
 	},
 	{
 		Name: "search_clicks", Kind: Authored, Lifetime: Retained,