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/migrations/0080_release_catalogue.down.sql

@@ -0,0 +1,5 @@
+DROP TABLE IF EXISTS mb_release_tracks;
+DROP TABLE IF EXISTS mb_releases;
+DROP TABLE IF EXISTS mb_artist_release_groups;
+DROP TABLE IF EXISTS mb_release_groups;
+DROP TABLE IF EXISTS mb_artists;

internal/db/migrations/0080_release_catalogue.up.sql

@@ -0,0 +1,86 @@
+-- 0080_release_catalogue.up.sql — Minstrel's own copy of what artists have
+-- released, read from MusicBrainz (Scribe milestone #502, #5519).
+--
+-- With Lidarr gone, the wanted list, search and import need to know an
+-- artist's discography and each release's track list. MusicBrainz allows one
+-- request a second, so what has been read is kept here and refreshed on a
+-- schedule rather than asked again for every page.
+--
+--   mb_artists                artists the catalogue has been asked about.
+--   mb_release_groups         what a person calls an album (Lidarr's albums
+--                             were release groups too), with MusicBrainz's
+--                             primary and secondary types.
+--   mb_artist_release_groups  who is credited on each group: a collaboration
+--                             belongs to every credited artist's discography.
+--   mb_releases               the editions of a group, read when something
+--                             needs a track list.
+--   mb_release_tracks         each release's track list.
+--
+-- Dates stay as MusicBrainz's partial-date text ("1997", "1997-05",
+-- "1997-05-21"): most early releases have only a year.
+
+CREATE TABLE mb_artists (
+    mbid                     text PRIMARY KEY,
+    name                     text NOT NULL,
+    sort_name                text NOT NULL DEFAULT '',
+    disambiguation           text NOT NULL DEFAULT '',
+    artist_type              text NOT NULL DEFAULT '',
+    country                  text NOT NULL DEFAULT '',
+    -- When the discography was last read in full; NULL means never.
+    discography_refreshed_at timestamptz,
+    created_at               timestamptz NOT NULL DEFAULT now(),
+    updated_at               timestamptz NOT NULL DEFAULT now()
+);
+
+CREATE INDEX mb_artists_refresh_idx ON mb_artists (discography_refreshed_at NULLS FIRST);
+
+CREATE TABLE mb_release_groups (
+    mbid                 text PRIMARY KEY,
+    title                text NOT NULL,
+    primary_type         text NOT NULL DEFAULT '',
+    secondary_types      text[] NOT NULL DEFAULT '{}',
+    first_release_date   text NOT NULL DEFAULT '',
+    artist_credit        text NOT NULL DEFAULT '',
+    -- When the releases and their track lists were last read; NULL means never.
+    releases_refreshed_at timestamptz,
+    created_at           timestamptz NOT NULL DEFAULT now(),
+    updated_at           timestamptz NOT NULL DEFAULT now()
+);
+
+CREATE TABLE mb_artist_release_groups (
+    artist_mbid        text NOT NULL REFERENCES mb_artists (mbid) ON DELETE CASCADE,
+    release_group_mbid text NOT NULL REFERENCES mb_release_groups (mbid) ON DELETE CASCADE,
+    PRIMARY KEY (artist_mbid, release_group_mbid)
+);
+
+CREATE INDEX mb_artist_release_groups_group_idx ON mb_artist_release_groups (release_group_mbid);
+
+CREATE TABLE mb_releases (
+    mbid               text PRIMARY KEY,
+    release_group_mbid text NOT NULL REFERENCES mb_release_groups (mbid) ON DELETE CASCADE,
+    title              text NOT NULL,
+    status             text NOT NULL DEFAULT '',
+    release_date       text NOT NULL DEFAULT '',
+    country            text NOT NULL DEFAULT '',
+    disambiguation     text NOT NULL DEFAULT '',
+    formats            text NOT NULL DEFAULT '',
+    track_count        integer NOT NULL DEFAULT 0,
+    created_at         timestamptz NOT NULL DEFAULT now()
+);
+
+CREATE INDEX mb_releases_group_idx ON mb_releases (release_group_mbid);
+
+CREATE TABLE mb_release_tracks (
+    release_mbid    text NOT NULL REFERENCES mb_releases (mbid) ON DELETE CASCADE,
+    medium_position integer NOT NULL,
+    position        integer NOT NULL,
+    medium_format   text NOT NULL DEFAULT '',
+    number          text NOT NULL DEFAULT '',
+    title           text NOT NULL,
+    length_ms       integer NOT NULL DEFAULT 0,
+    recording_mbid  text NOT NULL DEFAULT '',
+    PRIMARY KEY (release_mbid, medium_position, position)
+);
+
+CREATE INDEX mb_release_tracks_recording_idx ON mb_release_tracks (recording_mbid)
+    WHERE recording_mbid <> '';