feat(db): add query to count media items per visible library

Add GetVisibleLibraryMediaCounts, which returns the media item count for
each library visible to a given user in a single GROUP BY query over
media_items. It mirrors the visibility logic in GetUserVisibleLibraries
(libraries default to visible unless an explicit false row exists) so
counts can be resolved in one round-trip instead of N per-library
lookups.

Regenerated sqlc bindings (querier.go, queries.sql.go).

internal/database/queries.sql.go

@@ -7493,6 +7493,40 @@ func (q *Queries) GetUserVisibleLibraries(ctx context.Context, userID pgtype.UUI
 	return items, nil
 }
 
+const GetVisibleLibraryMediaCounts = `-- name: GetVisibleLibraryMediaCounts :many
+SELECT l.id, COUNT(mi.id) as media_count
+FROM libraries l
+LEFT JOIN library_visibility lv ON l.id = lv.library_id AND lv.user_id = $1
+LEFT JOIN media_items mi ON mi.library_id = l.id
+WHERE COALESCE(lv.is_visible, true) = true
+GROUP BY l.id
+`
+
+type GetVisibleLibraryMediaCountsRow struct {
+	ID         pgtype.UUID `db:"id" json:"id"`
+	MediaCount int64       `db:"media_count" json:"media_count"`
+}
+
+func (q *Queries) GetVisibleLibraryMediaCounts(ctx context.Context, userID pgtype.UUID) ([]GetVisibleLibraryMediaCountsRow, error) {
+	rows, err := q.db.Query(ctx, GetVisibleLibraryMediaCounts, userID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	items := []GetVisibleLibraryMediaCountsRow{}
+	for rows.Next() {
+		var i GetVisibleLibraryMediaCountsRow
+		if err := rows.Scan(&i.ID, &i.MediaCount); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const HasRecentConflictResolution = `-- name: HasRecentConflictResolution :one
 SELECT EXISTS(
     SELECT 1 FROM sync_conflicts