fix: address second code review findings

- Add CacheTTL default (24h) in config applyDefaults — without this,
  omitting cache_ttl from config silently defeats the entire caching
  mechanism (TTL=0 means cached data is never served)
- Fix pagination to use total Count instead of checking if last page
  was short — avoids wasting a rate-limit token when total count is
  an exact multiple of 100
- Preserve user-set IsIgnored flags across re-syncs — previously,
  DELETE+INSERT in the sync transaction reset all ignore flags to
  false, losing user preferences on every cache-expiry re-sync
- Check context cancellation on cache-hit code path — previously,
  ctx.Err() was not checked between cache check and returning cached
  data, violating the cancellation contract

internal/musicbrainz/api.go

@@ -56,8 +56,8 @@ func (c *MusicBrainzClient) GetArtistReleaseGroups(ctx context.Context, artistMB
 
 		allGroups = append(allGroups, parsed.ReleaseGroups...)
 
-		// If we got fewer results than the limit, we've reached the end
-		if len(parsed.ReleaseGroups) < limit {
+		// If we've fetched all results, we've reached the end.
+		if offset+len(parsed.ReleaseGroups) >= parsed.Count {
 			break
 		}
 		offset += limit