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

frontend/test/utils/queue-source-link.test.ts

@@ -1,11 +1,32 @@
-import { describe, expect, it, vi } from 'vitest';
+import { describe, expect, it, vi, beforeEach } from 'vitest';
 
 import {
   describeQueueSource,
   isQueueSourceNavigable,
   navigateToQueueSource,
 } from '@utils/queue-source-link';
+import { libraryStore } from '@store/library-store';
 import type { QueueSource } from '@store/queue-store';
+import { Events } from '../../src/events';
+import { emit, flush, stub } from '@test/support/harness';
+
+/**
+ * The albums the library cache holds for these tests: one tagged, one
+ * not, since which of the two an album is decides whether the album
+ * page opens on the catalog or says it is library-only.
+ */
+const ALBUMS = [
+  { ID: 7, Name: 'Scary Monsters', ArtistName: 'David Bowie', MBID: 'rg-7' },
+  { ID: 8, Name: 'Untagged', ArtistName: 'Nobody', MBID: '' },
+];
+
+/** Drop the cache and refill it, the way a scan completing does. */
+async function warmAlbumCache(): Promise<void> {
+  stub('library.Library.GetAlbums', ALBUMS);
+  emit(Events.LibraryScanComplete);
+  await flush();
+  await libraryStore.getAlbums();
+}
 
 describe('describeQueueSource', () => {
   it('returns null for an empty source', () => {
@@ -40,6 +61,10 @@ describe('isQueueSourceNavigable', () => {
 });
 
 describe('navigateToQueueSource', () => {
+  beforeEach(async () => {
+    await warmAlbumCache();
+  });
+
   function fireOn(source: QueueSource): unknown {
     const target = document.createElement('div');
     let detail: unknown;
@@ -53,10 +78,29 @@ describe('navigateToQueueSource', () => {
     return detail;
   }
 
-  it('builds the album navigate detail', () => {
-    expect(fireOn({ type: 'album', id: 7, label: 'Scary Monsters' })).toEqual(
-      { view: 'explore-album-details', localAlbumId: 7, albumName: 'Scary Monsters' },
-    );
+  it('builds the album navigate detail, carrying the release group MBID', () => {
+    expect(fireOn({ type: 'album', id: 7, label: 'Scary Monsters' })).toEqual({
+      view: 'explore-album-details',
+      localAlbumId: 7,
+      albumName: 'Scary Monsters',
+      releaseGroupMBID: 'rg-7',
+    });
+  });
+
+  it('omits the MBID for an untagged album, which really is library-only', () => {
+    expect(fireOn({ type: 'album', id: 8, label: 'Untagged' })).toEqual({
+      view: 'explore-album-details',
+      localAlbumId: 8,
+      albumName: 'Untagged',
+    });
+  });
+
+  it('omits the MBID for an album the cache does not know', () => {
+    expect(fireOn({ type: 'album', id: 99, label: 'Gone' })).toEqual({
+      view: 'explore-album-details',
+      localAlbumId: 99,
+      albumName: 'Gone',
+    });
   });
 
   it('builds the playlist navigate detail', () => {