Phase 1.13: add unmountGame export for chess — stops clock, destroys board,
nulls gameState on scene exit.

Phase 5.1: notification items now navigate to relevant section on click
(friends, play, tournaments, achievements based on type).

Phase 6.6: remove remaining stopDisconnectWatch calls from domino/ludo
since disconnect detection is now fully handled by match-session.js.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>