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/sync.go

@@ -39,6 +39,9 @@ func SyncArtistDiscography(
 
 	// Step 2: If we have cached data, return it.
 	if cachedCount > 0 {
+		if err := ctx.Err(); err != nil {
+			return nil, fmt.Errorf("sync artist discography: %w", err)
+		}
 		return database.GetExternalReleasesByArtistWithCache(db, artistMBID, ttl)
 	}
 
@@ -59,6 +62,23 @@ func SyncArtistDiscography(
 	}
 	defer tx.Rollback()
 
+	// Read existing ignore states before deleting to preserve user-set flags.
+	ignoredMap := map[string]bool{}
+	rows, err := tx.Query("SELECT rgid, is_ignored FROM external_releases WHERE artist_id = ?", artistMBID)
+	if err != nil {
+		return nil, fmt.Errorf("sync artist discography: query existing releases: %w", err)
+	}
+	for rows.Next() {
+		var rgid string
+		var ignored bool
+		if err := rows.Scan(&rgid, &ignored); err != nil {
+			rows.Close()
+			return nil, fmt.Errorf("sync artist discography: scan existing release: %w", err)
+		}
+		ignoredMap[rgid] = ignored
+	}
+	rows.Close()
+
 	// Delete old entries for this artist to avoid stale records.
 	if _, err := tx.Exec("DELETE FROM external_releases WHERE artist_id = ?", artistMBID); err != nil {
 		return nil, fmt.Errorf("sync artist discography: delete old releases: %w", err)
@@ -73,6 +93,10 @@ func SyncArtistDiscography(
 
 		ext := rg.ToExternalRelease()
 		ext.CachedAt = now
+		// Preserve user-set ignore flag from previous sync.
+		if ignored, ok := ignoredMap[ext.RGID]; ok {
+			ext.IsIgnored = ignored
+		}
 
 		cachedAtStr := ext.CachedAt.Format("2006-01-02 15:04:05")
 		if _, err := tx.Exec(