fix: A2 (relax art-source CHECK) + D + E integration residual

A2 — migration 0030: the albums/artists art `*_source` CHECK was a
fixed provider-ID allowlist fighting the extensible coverart.Register
registry (per-provider migration churn at 0016/0018/0020; rejected
test stub providers → ~11 enricher tests failed). Relax to "NULL or
non-empty"; the registry is the source of truth. Same brittleness
class as the #433 discovery-mix CHECK.

D — lidarr Approve resolves metadata/quality profiles (JSON arrays)
before the add; the test stubs returned {"id":1} for every path, so
ListMetadataProfiles failed to unmarshal → 500/Approve errors. Make
the lidarrrequests + admin_requests stubs path-aware (arrays for
/metadataprofile, /qualityprofile).

E:
- auth: requireUser (prelude.go) emitted code "auth_required"; the
  canonical code is "unauthenticated" (operator decision). Change the
  code; drop the now-dead "auth_required" web error-copy key
  ("unauthenticated" already has copy).
- playlists_system_test wrapped the real auth.RequireUser middleware
  but only injected withUser() context → 401. Like every other api
  handler test, drop the middleware and rely on requireUser().
- admin_users dup-username test seeded "test-existing" (seedUser
  prefixes) but POSTed "existing" → no collision; POST the prefixed
  name.
- me_timezone test decoded a top-level {"code"} but the envelope is
  {"error":{"code"}}; decode the nested shape.
- audit test asserted compact JSON; Postgres jsonb::text is spaced.
- put-lidarr-config tests predated the missing_defaults gate (correct
  handler behavior); supply the required defaults in the bodies.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/api/admin_lidarr_test.go

@@ -137,8 +137,9 @@ func TestHandlePutLidarrConfig_EmptyKeyPreservesSaved(t *testing.T) {
 		APIKey:  "originalkey",
 	})
 
-	// PUT with empty api_key — should preserve "originalkey".
-	body := []byte(`{"enabled":true,"base_url":"http://lidarr.lan:8686","api_key":""}`)
+	// PUT with empty api_key — should preserve "originalkey". enabled=true
+	// requires the defaults gate (missing_defaults) to be satisfied.
+	body := []byte(`{"enabled":true,"base_url":"http://lidarr.lan:8686","api_key":"","default_quality_profile_id":1,"default_metadata_profile_id":1,"default_root_folder_path":"/music"}`)
 	w := doAdminReq(t, h, http.MethodPut, "/api/admin/lidarr/config", body, admin)
 	if w.Code != http.StatusOK {
 		t.Fatalf("status = %d, want 200; body = %s", w.Code, w.Body.String())
@@ -183,7 +184,7 @@ func TestHandlePutLidarrConfig_HappyPath(t *testing.T) {
 	resetLidarrState(t, h)
 	admin := seedAdminUser(t, h)
 
-	body := []byte(`{"enabled":true,"base_url":"http://lidarr.lan:8686","api_key":"newkey","default_quality_profile_id":2,"default_root_folder_path":"/music"}`)
+	body := []byte(`{"enabled":true,"base_url":"http://lidarr.lan:8686","api_key":"newkey","default_quality_profile_id":2,"default_metadata_profile_id":1,"default_root_folder_path":"/music"}`)
 	w := doAdminReq(t, h, http.MethodPut, "/api/admin/lidarr/config", body, admin)
 	if w.Code != http.StatusOK {
 		t.Fatalf("status = %d, want 200; body = %s", w.Code, w.Body.String())