feat: Minstrel no longer talks to Lidarr: its connection, Delete via Lidarr and the unmonitor options are gone, and the track reports are plain quarantine (M502 #5525)

Migration 0091 drops lidarr_config and renames the quarantine tables, types,
indexes and the history column off the Lidarr name. The Integrations Lidarr
card, the Reports "Delete via Lidarr" action, the merge and remove-track
unmonitor options, the Lidarr audit actions and error codes go, on the
server, web and Android. The README describes acquisition as it is now.

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

internal/api/errors.go

@@ -67,3 +67,12 @@ func writeJSON(w http.ResponseWriter, status int, body any) {
 	w.WriteHeader(status)
 	_ = json.NewEncoder(w).Encode(body)
 }
+
+// writeAdminJSONErr writes a flat {"error":"<code>"} JSON response. This
+// mirrors the shape the RequireAdmin middleware uses and that the spec
+// defines for /api/admin/* errors.
+func writeAdminJSONErr(w http.ResponseWriter, status int, code string) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(map[string]string{"error": code})
+}