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/api/suggestions.go

@@ -1,21 +1,18 @@
 package api
 
 import (
-	"context"
 	"encoding/json"
 	"errors"
 	"io"
 	"net/http"
 	"strconv"
 	"strings"
-	"sync"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/jackc/pgx/v5/pgtype"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
-	"git.fabledsword.com/bvandeusen/minstrel/internal/lidarr"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/recommendation"
 )
 
@@ -31,10 +28,10 @@ type suggestionView struct {
 	// out-of-library artists is permanently partial (#2376), and the card
 	// falls back to the seed attribution it has always shown.
 	MatchedTags []string `json:"matched_tags,omitempty"`
-	// ImageURL is resolved on-demand from Lidarr (out-of-library
-	// artists have no local art row). Omitted when Lidarr is disabled
-	// or has no match — the client falls back to a placeholder. Not
-	// cached: a remote URL Lidarr surfaced, fetched by the browser.
+	// ImageURL is Minstrel's catalogue art endpoint for the candidate
+	// (out-of-library artists have no local art row, M502 #5519). It
+	// answers 404 when no enabled source has an image, and the client
+	// falls back to a placeholder.
 	ImageURL string `json:"image_url,omitempty"`
 }
 
@@ -105,7 +102,7 @@ func (h *handlers) handleListSuggestions(w http.ResponseWriter, r *http.Request)
 			MatchedTags: s.MatchedTags,
 		})
 	}
-	h.resolveSuggestionArt(r.Context(), out)
+	resolveSuggestionArt(out)
 	writeJSON(w, http.StatusOK, out)
 }
 
@@ -250,48 +247,15 @@ func (h *handlers) handleListSuggestionSnoozes(w http.ResponseWriter, r *http.Re
 	writeJSON(w, http.StatusOK, out)
 }
 
-// resolveSuggestionArt fills ImageURL on-demand from Lidarr's artist
-// lookup, matched by MBID (foreignArtistId). Best-effort and cache-free:
-// Lidarr is the only source — when it's disabled, unreachable, or has
-// no match for a candidate, that entry keeps an empty ImageURL and the
-// client renders its placeholder. Lookups run with bounded concurrency
-// so a full Discover page doesn't serialize ~12 round-trips. Never
-// fails the request; the suggestions list is the contract, art is a
-// nicety.
-func (h *handlers) resolveSuggestionArt(ctx context.Context, views []suggestionView) {
-	if len(views) == 0 {
-		return
-	}
-	cfg, err := h.lidarrCfg.Get(ctx)
-	if err != nil || !cfg.Enabled || cfg.BaseURL == "" || cfg.APIKey == "" {
-		return // Lidarr off / unconfigured → placeholders only
-	}
-	client := lidarr.NewClient(cfg.BaseURL, cfg.APIKey)
-
-	const maxConcurrent = 6
-	sem := make(chan struct{}, maxConcurrent)
-	var wg sync.WaitGroup
+// resolveSuggestionArt points each suggestion's ImageURL at Minstrel's
+// catalogue art endpoint (M502 #5519). Nothing is fetched here: the image is
+// looked up from the enabled cover-art sources when the browser asks for it,
+// and kept, so listing suggestions makes no outbound call. A candidate with
+// no MBID keeps an empty ImageURL and the client renders its placeholder.
+func resolveSuggestionArt(views []suggestionView) {
 	for i := range views {
-		if views[i].MBID == "" || views[i].Name == "" {
-			continue
+		if views[i].MBID != "" {
+			views[i].ImageURL = artistArtURL(views[i].MBID, views[i].Name)
 		}
-		wg.Add(1)
-		sem <- struct{}{}
-		go func(idx int) {
-			defer wg.Done()
-			defer func() { <-sem }()
-			results, lerr := client.LookupArtist(ctx, views[idx].Name)
-			if lerr != nil {
-				return // best-effort: no art on lookup failure
-			}
-			for _, res := range results {
-				if res.MBID == views[idx].MBID && res.ImageURL != "" {
-					// Distinct slice index per goroutine → race-free.
-					views[idx].ImageURL = res.ImageURL
-					return
-				}
-			}
-		}(i)
 	}
-	wg.Wait()
 }