Ludo multiplayer:
- Sync state to server on EVERY turn change (including no-valid-moves pass)
- Use turn_count to detect stale vs fresh server state (prevents re-processing)
- Non-host players poll at 1.5s and receive dice rolls + board state
- Bot turns run only on host, results synced to server for other players
- Fix double-encoding of game_state/positions in API
- Play notification sound when turn returns to player

Chess multiplayer:
- Detect move type (check/capture/castle) from FEN diff on received moves
- Show check highlight (red king square) for opponent's checking moves
- Play correct SFX (check/capture/castle) instead of generic 'move'
- Show last-move highlight squares for received moves
- Skip polling during recovery to prevent SFX burst on reconnect
- Track captured pieces from opponent's moves
- Sync move list from server history
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>