feat: a release catalogue from MusicBrainz; request search asks it directly (M502 #5519)

Minstrel keeps its own record of what artists have released, read from
MusicBrainz, so the wanted list, search and import no longer need Lidarr.

- internal/musicbrainz: searches (artists, release groups, recordings) and
  browses (an artist's release groups; a group's releases with track lists).
  One process-wide pacer at 1.1s, shared with tag enrichment, because
  MusicBrainz's limit is per address. A 503 throttle is retried.
- Migration 0080: mb_artists, mb_release_groups, mb_artist_release_groups
  (a collaboration belongs to each credited artist), mb_releases,
  mb_release_tracks.
- internal/catalogue: Discography and Releases serve the held copy and
  re-read it when older than 7 or 30 days. An unreachable MusicBrainz
  serves the stale copy, marked. An hourly pass re-reads due artists.
- Art for what isn't held comes through /api/catalogue/art from the
  enabled cover-art sources (Cover Art Archive by release group, then the
  name-based sources) and is kept on disk, so the browser never fetches a
  third-party host. A miss is a 404 and the card shows its icon.
- Request search moves from /api/lidarr/search to /api/catalogue/search,
  with the same response shape. Albums are release groups, and "in
  library" matches albums.release_group_mbid. A 10-minute cache absorbs
  search-as-you-type. Discover suggestions point at the art endpoint
  instead of looking up Lidarr.
- Android calls the new path and loads Discover art through ServerImage.
  Installed builds older than this one lose Discover search until they
  update (no compatibility path, rule 22).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/db/dbq/models.go

@@ -482,6 +482,59 @@ type LoudnessSetting struct {
 	LeveledCacheMb      int32
 }
 
+type MbArtist struct {
+	Mbid                   string
+	Name                   string
+	SortName               string
+	Disambiguation         string
+	ArtistType             string
+	Country                string
+	DiscographyRefreshedAt pgtype.Timestamptz
+	CreatedAt              pgtype.Timestamptz
+	UpdatedAt              pgtype.Timestamptz
+}
+
+type MbArtistReleaseGroup struct {
+	ArtistMbid       string
+	ReleaseGroupMbid string
+}
+
+type MbRelease struct {
+	Mbid             string
+	ReleaseGroupMbid string
+	Title            string
+	Status           string
+	ReleaseDate      string
+	Country          string
+	Disambiguation   string
+	Formats          string
+	TrackCount       int32
+	CreatedAt        pgtype.Timestamptz
+}
+
+type MbReleaseGroup struct {
+	Mbid                string
+	Title               string
+	PrimaryType         string
+	SecondaryTypes      []string
+	FirstReleaseDate    string
+	ArtistCredit        string
+	ReleasesRefreshedAt pgtype.Timestamptz
+	CreatedAt           pgtype.Timestamptz
+	UpdatedAt           pgtype.Timestamptz
+}
+
+type MbReleaseTrack struct {
+	ReleaseMbid    string
+	MediumPosition int32
+	Position       int32
+	MediumFormat   string
+	Number         string
+	Title          string
+	LengthMs       int32
+	RecordingMbid  string
+}
+
 type MissingReacquisition struct {
 	AlbumID       pgtype.UUID
 	Attempts      int32