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/components/album-actions.test.ts

@@ -18,7 +18,7 @@ import { describe, expect, it, beforeEach } from 'vitest';
 import type { LitElement } from 'lit';
 
 import '@components/explore-album-details/explore-album-details';
-import { stub, flush, resetHarness, calls } from '@test/support/harness';
+import { stub, flush, resetHarness, calls, lastArgs } from '@test/support/harness';
 import { fixture, shadow, shadowAll, text } from '@test/support/render';
 
 type Version = {
@@ -52,6 +52,12 @@ function track(n: number, owned: boolean) {
  * The component builds its versions from fetched releases; this reaches
  * past that and sets the state the header actually reads, which is the
  * only part under test here.
+ *
+ * Owning a track means the library has a *file* for it — the page
+ * resolves the displayed tracklist's paths once and every action, badge
+ * and dimmed row reads that one answer. So the fixture says which
+ * tracks have files rather than setting an `inLibrary` flag, which is
+ * what used to be able to claim ownership of something unplayable.
  */
 async function withVersion(
   owned: number,
@@ -61,11 +67,20 @@ async function withVersion(
     albumName: 'Glass Harbour',
   });
 
+  const tracks = Array.from({ length: total }, (_, i) => track(i + 1, i < owned));
+
+  const paths: Record<string, string[]> = {};
+  for (const t of tracks.filter((t) => t.inLibrary)) {
+    paths[t.mbid] = [`/music/${t.mbid}.mp3`];
+  }
+
+  stub('library.Library.GetFilePathsByRecordingMBIDs', paths);
+
   const version: Version = {
     key: 'v1',
     label: '2019',
     sublabel: `${total} tracks`,
-    tracks: Array.from({ length: total }, (_, i) => track(i + 1, i < owned)),
+    tracks,
   };
 
   Object.assign(el, {
@@ -125,23 +140,28 @@ describe('the album header’s primary action', () => {
     expect(shadow(el, '[data-testid="album-queue"]')).toBeNull();
   });
 
-  it('asks for the owned tracks’ paths once, by the key it owns them by', async () => {
-    // `perf.m2`'s rule: ask for what the caller uses, once. The caller
-    // here uses file paths and knows its tracks only as recording
-    // MBIDs — `MBTrack.localId` is declared and never written by
-    // anything in the backend.
+  it('asks for the tracklist’s paths once, on load, and not on click', async () => {
+    // `perf.m2`'s rule — ask for what the caller uses, once — and the
+    // ownership rule with it. The page asks about the *whole* displayed
+    // tracklist when it settles, because whether a track is owned is
+    // that query's answer and not something to be inferred first. Every
+    // action, badge and dimmed row then reads the one result, so a
+    // click asks nothing and cannot fail.
     const el = await withVersion(7, 12);
 
+    const onLoad = calls('library.Library.GetFilePathsByRecordingMBIDs');
+
+    expect(onLoad).toHaveLength(1);
+    expect(onLoad[0]!.args[0]).toHaveLength(12);
+    // No empty MBID — an empty string matches every untagged recording
+    // in the library.
+    expect(onLoad[0]!.args[0]).not.toContain('');
+
     shadow<HTMLElement>(el, '[data-testid="album-play"]')!.click();
     await flush();
 
-    const asked = calls('library.Library.GetFilePathsByRecordingMBIDs');
-
-    expect(asked).toHaveLength(1);
-    // Only the owned ones, and no empty MBID — an empty string matches
-    // every untagged recording in the library.
-    expect(asked[0]!.args[0]).toHaveLength(7);
-    expect(asked[0]!.args[0]).not.toContain('');
+    expect(calls('library.Library.GetFilePathsByRecordingMBIDs')).toHaveLength(1);
+    expect(lastArgs('queue.Queue.SetQueue')?.[0]).toHaveLength(7);
   });
 });