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/phantom-resolver.test.ts

@@ -0,0 +1,201 @@
+/**
+ * The phantom resolver showed the same library track twice.
+ *
+ * Its right-hand panel renders two lists one under the other — the
+ * scored candidates and the library search results — and a search for
+ * the obvious title returns exactly what scoring already found. So the
+ * track appeared once with a score and once without, and double-clicking
+ * either did the same thing.
+ *
+ * The second half is what a match *means*: one library file cannot stand
+ * in for two unmatched tracks, or applying adds it to the playlist
+ * twice. `FindPhantomMatches` has always claimed candidates on the
+ * auto-match path; the manual path had no such rule.
+ */
+import { beforeEach, describe, expect, it } from 'vitest';
+import type { LitElement } from 'lit';
+
+import '@components/phantom-resolver/phantom-resolver';
+import { flush, stub } from '@test/support/harness';
+import { fixture } from '@test/support/render';
+
+interface Candidate {
+  FilePath: string;
+  Title: string;
+  Artist: string;
+  Album: string;
+  Duration: string;
+  Score: number;
+}
+
+function candidate(
+  path: string,
+  title: string,
+  score = 0.5,
+): Candidate {
+  return {
+    FilePath: path,
+    Title: title,
+    Artist: 'An Artist',
+    Album: 'An Album',
+    Duration: '200000',
+    Score: score,
+  };
+}
+
+const PHANTOM_A = '/music/gone/one.mp3';
+const PHANTOM_B = '/music/gone/two.mp3';
+
+/** Mount the dialog with two unmatched tracks and no auto-matches. */
+async function open(
+  candidates: Candidate[],
+  searchResults: Candidate[] = [],
+): Promise<HTMLElement & { updateComplete: Promise<unknown> }> {
+  stub('playlist.Service.FindPhantomMatches', {
+    AutoMatched: [],
+    Unmatched: [PHANTOM_A, PHANTOM_B],
+  });
+  stub('playlist.Service.GetPhantomCandidates', candidates);
+  stub('playlist.Service.SearchLibrary', searchResults);
+
+  const el = await fixture<
+    LitElement & { show(id: number, tracks: unknown[]): void }
+  >('phantom-resolver');
+
+  el.show(1, [
+    { FilePath: PHANTOM_A, Title: 'One', Phantom: true },
+    { FilePath: PHANTOM_B, Title: 'Two', Phantom: true },
+  ]);
+
+  await flush();
+  await el.updateComplete;
+  await flush();
+  await el.updateComplete;
+
+  return el;
+}
+
+function candidateRows(el: HTMLElement): HTMLElement[] {
+  return [
+    ...(el.shadowRoot?.querySelectorAll<HTMLElement>('.candidate-item') ?? []),
+  ];
+}
+
+/** The dialog renders the file path as each row's `title`. */
+function rowPaths(el: HTMLElement): string[] {
+  return candidateRows(el).map((r) => r.getAttribute('title') ?? '');
+}
+
+describe('the phantom resolver', () => {
+  beforeEach(() => {
+    stub('playlist.Service.ResolvePhantomTracks', null);
+    stub('playlist.Service.RemovePhantomTracks', null);
+  });
+
+  it('lists a search result the candidates already show only once', async () => {
+    const shared = candidate('/music/have/one.mp3', 'One', 0.7);
+    const el = await open([shared], [shared, candidate('/music/have/x.mp3', 'X', 0)]);
+
+    // Type into the search box and let the debounce fire.
+    const input = el.shadowRoot?.querySelector<HTMLInputElement>(
+      '.search-input',
+    );
+
+    expect(input, 'the search box is rendered').toBeTruthy();
+
+    input!.value = 'one';
+    input!.dispatchEvent(new InputEvent('input', { bubbles: true }));
+
+    await new Promise((r) => setTimeout(r, 500));
+    await flush();
+    await el.updateComplete;
+
+    const paths = rowPaths(el);
+
+    expect(paths.filter((p) => p === shared.FilePath)).toHaveLength(1);
+    expect(paths).toContain('/music/have/x.mp3');
+  });
+
+  it('matches a candidate from the keyboard, not only a double-click', async () => {
+    const el = await open([candidate('/music/have/one.mp3', 'One', 0.7)]);
+    const row = candidateRows(el)[0];
+
+    expect(row, 'a candidate row is rendered').toBeTruthy();
+    expect(row!.getAttribute('role')).toBe('button');
+    expect(row!.getAttribute('tabindex')).toBe('0');
+
+    row!.dispatchEvent(
+      new KeyboardEvent('keydown', { key: 'Enter', bubbles: true }),
+    );
+    await el.updateComplete;
+
+    // Matching the first phantom advances to the second, whose row
+    // shows the check mark for the one just confirmed.
+    const matched = el.shadowRoot?.querySelectorAll('.phantom-item.matched');
+
+    expect(matched).toHaveLength(1);
+  });
+
+  it('will not spend one library file on two unmatched tracks', async () => {
+    const only = candidate('/music/have/one.mp3', 'One', 0.7);
+    const el = await open([only]);
+
+    candidateRows(el)[0]!.dispatchEvent(
+      new KeyboardEvent('keydown', { key: 'Enter', bubbles: true }),
+    );
+    await el.updateComplete;
+    await flush();
+    await el.updateComplete;
+
+    // The second phantom is selected now and offered the same file,
+    // which is already standing in for the first.
+    const row = candidateRows(el)[0];
+
+    expect(row!.classList.contains('claimed')).toBe(true);
+    expect(row!.getAttribute('aria-disabled')).toBe('true');
+
+    row!.dispatchEvent(
+      new KeyboardEvent('keydown', { key: 'Enter', bubbles: true }),
+    );
+    await el.updateComplete;
+
+    // Still one confirmed match, not two.
+    expect(
+      el.shadowRoot?.querySelectorAll('.phantom-item.matched'),
+    ).toHaveLength(1);
+  });
+
+  it('gives the auto-match disclosure a keyboard-reachable control', async () => {
+    stub('playlist.Service.FindPhantomMatches', {
+      AutoMatched: [
+        {
+          PhantomPath: PHANTOM_A,
+          PhantomTitle: 'One',
+          Candidate: candidate('/music/have/one.mp3', 'One', 0.95),
+        },
+      ],
+      Unmatched: [PHANTOM_B],
+    });
+    stub('playlist.Service.GetPhantomCandidates', []);
+
+    const el = await fixture<
+      LitElement & { show(id: number, tracks: unknown[]): void }
+    >('phantom-resolver');
+
+    el.show(1, [{ FilePath: PHANTOM_A, Title: 'One', Phantom: true }]);
+    await flush();
+    await el.updateComplete;
+
+    const header = el.shadowRoot?.querySelector('.auto-match-header');
+
+    expect(header?.tagName).toBe('BUTTON');
+    expect(header?.getAttribute('aria-expanded')).toBe('false');
+
+    // aria-controls has to name an element that is in the DOM, so the
+    // list renders collapsed rather than not at all.
+    const controls = header?.getAttribute('aria-controls');
+
+    expect(controls).toBeTruthy();
+    expect(el.shadowRoot?.getElementById(controls!)).toBeTruthy();
+  });
+});