Add kick player and leave game functionality

- Host can kick players from lobby (removes from game, clears presenter if needed)
- Client can voluntarily leave game
- Fix browser-compatible base64 decoding for document upload (atob vs Buffer)

hooks/useGame.ts

@@ -1446,6 +1446,31 @@ export const useGame = () => {
     if (data.type === 'PRESENTER_CHANGED') {
         setPresenterId(data.payload.presenterId);
     }
+    
+    if (data.type === 'KICKED') {
+        if (hostConnectionRef.current) {
+          hostConnectionRef.current.close();
+          hostConnectionRef.current = null;
+        }
+        if (peerRef.current) {
+          peerRef.current.destroy();
+          peerRef.current = null;
+        }
+        clearStoredSession();
+        if (timerRef.current) clearInterval(timerRef.current);
+        setError(data.payload.reason || 'You were kicked from the game');
+        setGamePin(null);
+        setQuiz(null);
+        setPlayers([]);
+        setCurrentPlayerId(null);
+        setCurrentPlayerName(null);
+        setGameState('LANDING');
+        navigate('/', { replace: true });
+    }
+    
+    if (data.type === 'PLAYER_LEFT') {
+        setPlayers(prev => prev.filter(p => p.id !== data.payload.playerId));
+    }
   };
 
   const handleAnswer = (arg: boolean | AnswerOption) => {
@@ -1535,6 +1560,54 @@ export const useGame = () => {
     broadcast({ type: 'PRESENTER_CHANGED', payload: { presenterId: playerId } });
   };
 
+  const kickPlayer = (playerId: string) => {
+    if (role !== 'HOST') return;
+    if (playerId === 'host') return;
+    
+    const conn = connectionsRef.current.get(playerId);
+    if (conn?.open) {
+      conn.send({ type: 'KICKED', payload: { reason: 'You were kicked by the host' } });
+      conn.close();
+    }
+    connectionsRef.current.delete(playerId);
+    
+    const updatedPlayers = playersRef.current.filter(p => p.id !== playerId);
+    playersRef.current = updatedPlayers;
+    setPlayers(updatedPlayers);
+    
+    if (presenterIdRef.current === playerId) {
+      setPresenterId(null);
+      broadcast({ type: 'PRESENTER_CHANGED', payload: { presenterId: null } });
+    }
+    
+    broadcast({ type: 'PLAYER_LEFT', payload: { playerId } });
+  };
+
+  const leaveGame = () => {
+    if (role !== 'CLIENT') return;
+    
+    if (hostConnectionRef.current?.open) {
+      hostConnectionRef.current.close();
+    }
+    hostConnectionRef.current = null;
+    
+    if (peerRef.current) {
+      peerRef.current.destroy();
+      peerRef.current = null;
+    }
+    
+    clearStoredSession();
+    if (timerRef.current) clearInterval(timerRef.current);
+    
+    setGamePin(null);
+    setQuiz(null);
+    setPlayers([]);
+    setCurrentPlayerId(null);
+    setCurrentPlayerName(null);
+    setGameState('LANDING');
+    navigate('/', { replace: true });
+  };
+
   const sendAdvance = (action: 'START' | 'NEXT' | 'SCOREBOARD') => {
     if (role !== 'CLIENT' || !hostConnectionRef.current) return;
     hostConnectionRef.current.send({ type: 'ADVANCE', payload: { action } });
@@ -1544,6 +1617,6 @@ export const useGame = () => {
     role, gameState, quiz, players, currentQuestionIndex, timeLeft, error, gamePin, hasAnswered, lastPointsEarned, lastAnswerCorrect, currentCorrectShape, selectedOption, currentPlayerScore, currentStreak, currentPlayerId, gameConfig,
     pendingQuizToSave, dismissSavePrompt, sourceQuizId, isReconnecting, currentPlayerName, presenterId,
     startQuizGen, startManualCreation, cancelCreation, finalizeManualQuiz, loadSavedQuiz, joinGame, startGame: startHostGame, handleAnswer, nextQuestion, showScoreboard,
-    updateQuizFromEditor, startGameFromEditor, backFromEditor, endGame, attemptReconnect, goHomeFromDisconnected, resumeGame, setPresenterPlayer, sendAdvance
+    updateQuizFromEditor, startGameFromEditor, backFromEditor, endGame, attemptReconnect, goHomeFromDisconnected, resumeGame, setPresenterPlayer, sendAdvance, kickPlayer, leaveGame
   };
 };