fix: use 'client output queue' terminology consistently

Replace ambiguous 'queue' with 'client output queue' throughout
documentation, code comments, log messages, and error strings
added in the queue pruning PR.

internal/db/queries.go

@@ -1110,8 +1110,8 @@ func (database *Database) GetSessionCreatedAt(
 	return createdAt, nil
 }
 
-// PruneOldQueueEntries deletes client_queues rows older
-// than cutoff and returns the number of rows removed.
+// PruneOldQueueEntries deletes client output queue entries
+// older than cutoff and returns the number of rows removed.
 func (database *Database) PruneOldQueueEntries(
 	ctx context.Context,
 	cutoff time.Time,
@@ -1122,7 +1122,7 @@ func (database *Database) PruneOldQueueEntries(
 	)
 	if err != nil {
 		return 0, fmt.Errorf(
-			"prune old queue entries: %w", err,
+			"prune old client output queue entries: %w", err,
 		)
 	}