requestBotMove retried forever on failure and did nothing at all when the engine
answered without a move, so a Stockfish hiccup left the player watching the
thinking indicator with no way to continue.

Now: four attempts with exponential backoff, then a dialog offering to end the
game. Also guards against gameState having been torn down mid-request.

The engine itself is healthy — verified live: GET /api/chess/bots returns the
seven bots the client expects, and POST /api/chess/move answers the start
position with d2d4 at depth 3. api/bots.php's paths are correct.

Arabic and English strings added for the new message.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>