fix: address code review findings

- Honor ignore_singles/ignore_compilations at scanner read time so toggles
  take effect immediately on the dashboard, artist page, and digest instead
  of waiting for the MusicBrainz cache to expire and prune rows.
- Run notifier notify synchronously in the scheduler loop to avoid overlapping
  read-send-mark runs double-sending the digest.
- Show artist name (with ID fallback) on the archive page instead of raw IDs.
- Select last_synced in GetAllArtistSettings for contract consistency.
- Fix stale startPeriodicSync comment and remove redundant error var.
- Remove dead ignored-branch from the artist template (never rendered).
- Add tests: CSRF sameOrigin, ArtistCacheFresh, secondary_types round-trip,
  and scanner type-toggle filtering.
- Update Specification.md schema/config to reflect mbid, last_synced,
  secondary_types, sync.interval, and server.public_url.

internal/database/artist_settings.go

@@ -89,7 +89,7 @@ func nullIfEmpty(s string) interface{} {
 // GetAllArtistSettings returns all rows from artist_settings.
 func GetAllArtistSettings(db *DB) ([]ArtistSettings, error) {
 	rows, err := db.Conn().Query(
-		"SELECT id, name, mbid, ignore_singles, ignore_compilations, monitored FROM artist_settings",
+		"SELECT id, name, mbid, ignore_singles, ignore_compilations, monitored, last_synced FROM artist_settings",
 	)
 	if err != nil {
 		return nil, fmt.Errorf("query all artist settings: %w", err)
@@ -100,10 +100,14 @@ func GetAllArtistSettings(db *DB) ([]ArtistSettings, error) {
 	for rows.Next() {
 		var s ArtistSettings
 		var mbid sql.NullString
-		if err := rows.Scan(&s.ID, &s.Name, &mbid, &s.IgnoreSingles, &s.IgnoreCompilations, &s.Monitored); err != nil {
+		var lastSynced sql.NullTime
+		if err := rows.Scan(&s.ID, &s.Name, &mbid, &s.IgnoreSingles, &s.IgnoreCompilations, &s.Monitored, &lastSynced); err != nil {
 			return nil, fmt.Errorf("scan artist settings: %w", err)
 		}
 		s.MBID = mbid.String
+		if lastSynced.Valid {
+			s.LastSynced = lastSynced.Time
+		}
 		results = append(results, s)
 	}
 	if err := rows.Err(); err != nil {