fix(db): check both name and target_format in default transcodings migration (#5175)

The ensure_default_transcodings migration only checked target_format
before inserting, but the transcoding table has UNIQUE constraints on
both name and target_format. Older installations may have entries where
the name matches a default (e.g., 'opus audio') but the target_format
differs (e.g., 'oga' instead of 'opus'), causing a UNIQUE constraint
violation on name during the INSERT.

Fixes #5174

db/migrations/20260309203355_ensure_default_transcodings.go

@@ -17,9 +17,12 @@ func upEnsureDefaultTranscodings(_ context.Context, tx *sql.Tx) error {
 	// Older installations may be missing default transcodings that were added
 	// after the initial seeding (e.g., aac was added later than mp3/opus).
 	// Insert any missing defaults without touching user-customized entries.
+	// Check both target_format and name since both have UNIQUE constraints,
+	// and older entries may have a different target_format (e.g., 'oga' vs 'opus')
+	// but the same name.
 	for _, t := range consts.DefaultTranscodings {
 		var count int
-		err := tx.QueryRow("SELECT COUNT(*) FROM transcoding WHERE target_format = ?", t.TargetFormat).Scan(&count)
+		err := tx.QueryRow("SELECT COUNT(*) FROM transcoding WHERE target_format = ? OR name = ?", t.TargetFormat, t.Name).Scan(&count)
 		if err != nil {
 			return err
 		}