Add spectator watch page, forfeit-on-new-game, CPU self-play, and threefold repetition

- /watch live feed of active games with click-to-fullscreen and per-game back button
- Starting a new game forfeits the in-progress game; opponent is flagged the winner
- Watch CPU vs CPU self-play games; results shown for ~30s before cleanup
- Detect threefold repetition in the C# rules layer and end the game as a draw

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

JoshHeaps.Net/wwwroot/js/ChessScripts/ChessSignalR.js

@@ -15,6 +15,10 @@ const ChessSignalR = {
             await this.handleMoveUpdate(gameId, moveDto, moveResultDto);
         });
 
+        this.connection.on("ReceiveGameOver", async (gameId, winner, reason) => {
+            await this.handleGameOver(gameId, winner, reason);
+        });
+
         try {
             await this.connection.start();
             console.log("✅ SignalR connected");
@@ -34,6 +38,17 @@ const ChessSignalR = {
         ChessAPI.alertGameStatusChange(moveResultDto);
     },
 
+    async handleGameOver(gameId, winner, reason) {
+        if (gameId !== GameState.currentGameId) return;
+
+        const youWon = (winner === "White") === GameState.currentPlayerIsWhite;
+
+        if (reason === "forfeit")
+            alert(youWon ? "🏳️ Your opponent forfeited — you win!" : "🏳️ You forfeited this game.");
+
+        await this.leaveGame();
+    },
+
     async notifyMoveMade(moveDto, moveResult) {
         if (this.connection) {
             await this.connection.invoke("MoveMade", GameState.currentGameId, moveDto, moveResult);