fix(db): clarify lidarr_requests query semantics

- HasNonTerminalRequestForMBID: use named parameter @mbid so the
  generated Go signature is `mbid string` instead of the misleading
  `lidarrArtistMbid string` (the value applies to all three MBID
  columns, not just the artist column)
- CancelLidarrRequest: comment dual role of $2 (ownership guard +
  decided_by audit field) for future readers
- CompleteLidarrRequest: document the per-kind one-of-three contract
  for matched_*_id parameters

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/db/dbq/lidarr_requests.sql.go

@@ -80,6 +80,11 @@ type CancelLidarrRequestParams struct {
 	DecidedBy pgtype.UUID
 }
 
+// $2 serves as both the ownership guard (user_id = $2) and the
+// decided_by audit field. The generated parameter struct names it
+// DecidedBy — callers must pass the cancelling user's UUID, and
+// a wrong UUID will silently no-op (zero rows updated) rather than
+// erroring at the SQL layer.
 func (q *Queries) CancelLidarrRequest(ctx context.Context, arg CancelLidarrRequestParams) (LidarrRequest, error) {
 	row := q.db.QueryRow(ctx, cancelLidarrRequest, arg.ID, arg.DecidedBy)
 	var i LidarrRequest
@@ -129,7 +134,11 @@ type CompleteLidarrRequestParams struct {
 }
 
 // Reconciler transitions an approved request to completed when its
-// target track/album/artist has appeared in the library.
+// target track/album/artist has appeared in the library. Callers
+// should set ONLY the matched_*_id corresponding to the request's
+// kind and pass pgtype.UUID{} (Valid: false) for the others —
+// per-kind one-of-three is the contract, NULL for the others
+// preserves auditability if the matched row is later evicted.
 func (q *Queries) CompleteLidarrRequest(ctx context.Context, arg CompleteLidarrRequestParams) (LidarrRequest, error) {
 	row := q.db.QueryRow(ctx, completeLidarrRequest,
 		arg.ID,
@@ -268,9 +277,10 @@ SELECT EXISTS (
 // Returns true if any user has a pending/approved/completed request
 // whose MBID matches at the given level. Used to set the `requested`
 // flag on /api/lidarr/search responses. Terminal-status (rejected,
-// failed) rows do not count.
-func (q *Queries) HasNonTerminalRequestForMBID(ctx context.Context, lidarrArtistMbid string) (bool, error) {
-	row := q.db.QueryRow(ctx, hasNonTerminalRequestForMBID, lidarrArtistMbid)
+// failed) rows do not count. The same MBID parameter is checked
+// against artist/album/track columns based on kind.
+func (q *Queries) HasNonTerminalRequestForMBID(ctx context.Context, mbid string) (bool, error) {
+	row := q.db.QueryRow(ctx, hasNonTerminalRequestForMBID, mbid)
 	var exists bool
 	err := row.Scan(&exists)
 	return exists, err