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/completeness_test.go

@@ -1,12 +1,15 @@
 package library
 
 import (
+	"fmt"
 	"testing"
+
+	"yellowjacket/backend/database"
 )
 
-// track is one row of release_group_recordings as the scan would write
-// it: a position on a disc, and whatever total the file's tag declared
-// (0 meaning the tag did not say).
+// track is one file as the scan would write it: a position on a disc,
+// and whatever total the file's tag declared (0 meaning the tag did not
+// say).
 type track struct {
 	recordingID int
 	disc        int
@@ -14,58 +17,37 @@ type track struct {
 	total       int
 }
 
-// stageAlbum writes an album's tracks straight into
-// release_group_recordings.  The completeness query reads only that
-// table, so this exercises the arithmetic without standing up a scan.
+// stageAlbum writes an album's files straight in.  The completeness
+// query reads only audio_files now - the totals used to live on a join
+// table - so this exercises the arithmetic without standing up a scan.
 func stageAlbum(t *testing.T, lib *Library, albumID int, tracks []track) {
 	t.Helper()
 
-	// The foreign keys are enforced, so the album and its recordings
-	// have to exist before they can be linked.
-	if _, err := lib.db.ExecContext(
-		`INSERT INTO artist_credit (id, text) VALUES (1, 'Test Artist')`,
-	); err != nil {
-		t.Fatalf("staging artist credit: %v", err)
-	}
-
-	if _, err := lib.db.ExecContext(
-		`INSERT INTO release_groups (id, name, album_artist_credit_id)
-		 VALUES (?, ?, 1)`,
-		albumID, "Test Album",
-	); err != nil {
-		t.Fatalf("staging album: %v", err)
-	}
-
 	for _, tr := range tracks {
-		if _, err := lib.db.ExecContext(
-			`INSERT INTO recordings (id, name, artist_credit_id) VALUES (?, ?, 1)`,
-			tr.recordingID, "Test Track",
-		); err != nil {
-			t.Fatalf("staging recording %d: %v", tr.recordingID, err)
-		}
+		database.InsertTestTrack(t, lib.db, database.TestTrack{
+			FilePath:    fmt.Sprintf("/music/album%d/%d.mp3", albumID, tr.recordingID),
+			Title:       "Test Track",
+			Artist:      "Test Artist",
+			Album:       fmt.Sprintf("Test Album %d", albumID),
+			TrackNumber: int64(tr.number),
+			DiscNumber:  int64(tr.disc),
+			TotalTracks: int64(tr.total),
+		})
+	}
+}
+
+// albumIDFor reads back the id stageAlbum's files were filed under.
+func albumIDFor(t *testing.T, lib *Library, albumID int) int64 {
+	t.Helper()
+
+	var id int64
+	if err := lib.db.QueryRowWriter(
+		"SELECT id FROM albums WHERE name = ?", fmt.Sprintf("Test Album %d", albumID),
+	).Scan(&id); err != nil {
+		t.Fatalf("read album id: %v", err)
 	}
 
-	for _, tr := range tracks {
-		var total any
-		if tr.total > 0 {
-			total = tr.total
-		}
-
-		var number any
-		if tr.number > 0 {
-			number = tr.number
-		}
-
-		_, err := lib.db.ExecContext(
-			`INSERT INTO release_group_recordings
-			   (release_group_id, recording_id, track_number, disc_number, total_tracks)
-			 VALUES (?, ?, ?, ?, ?)`,
-			albumID, tr.recordingID, number, tr.disc, total,
-		)
-		if err != nil {
-			t.Fatalf("staging track %d: %v", tr.recordingID, err)
-		}
-	}
+	return id
 }
 
 // disc builds a run of tracks on one disc, each declaring the same
@@ -210,7 +192,7 @@ func TestGetAlbumCompleteness(t *testing.T) {
 
 			stageAlbum(t, lib, albumID, tc.tracks)
 
-			got, err := lib.GetAlbumCompleteness(int64(albumID))
+			got, err := lib.GetAlbumCompleteness(albumIDFor(t, lib, albumID))
 			if err != nil {
 				t.Fatalf("GetAlbumCompleteness: %v", err)
 			}