Remove vote on leave/disconnect, require 2+ members, restore vote on sync

- Add removeVote (only during VOTING state, preserves revealed votes)
- Remove user's vote on disconnect, room:leave, and kick
- After vote removal, check auto-reveal for remaining members
- Send poker:my-vote on sync so card selection is restored
- Disable voting cards until at least 2 participants are present

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/PokerRoom.jsx

@@ -60,21 +60,32 @@ export default function PokerRoom({ session, issue, user, members, roomId, onSav
       setError(payload?.error || 'Unexpected poker error');
     }
 
+    function onMyVote(payload) {
+      if (payload.sessionId !== session.id) return;
+      if (payload.vote !== null && payload.vote !== undefined) {
+        setMyVote(payload.vote);
+      }
+    }
+
     socket.on('poker:vote-update', onVoteUpdate);
     socket.on('poker:revealed', onRevealed);
     socket.on('poker:saved', onSavedPayload);
     socket.on('poker:error', onError);
+    socket.on('poker:my-vote', onMyVote);
 
     return () => {
       socket.off('poker:vote-update', onVoteUpdate);
       socket.off('poker:revealed', onRevealed);
       socket.off('poker:saved', onSavedPayload);
       socket.off('poker:error', onError);
+      socket.off('poker:my-vote', onMyVote);
     };
   }, [session.id, socket]);
 
+  const canVote = !revealed && members.length >= 2;
+
   function handleVote(value) {
-    if (revealed) return;
+    if (!canVote) return;
     setMyVote(value);
     socket.emit('poker:vote', {
       sessionId: session.id,
@@ -162,14 +173,18 @@ export default function PokerRoom({ session, issue, user, members, roomId, onSav
             </div>
           ) : (
             <div className="space-y-3">
-              <div className="grid grid-cols-7 gap-2">
+              {!canVote && members.length < 2 && (
+                <p className="text-sm text-slate-400 text-center m-0">Waiting for at least 2 participants to start voting...</p>
+              )}
+              <div className={`grid grid-cols-7 gap-2${!canVote ? ' opacity-50 pointer-events-none' : ''}`}>
                 {CARDS.map((card) => {
                   const isSelected = myVote === card.value;
                   return (
                     <button
                       key={card.value}
                       onClick={() => handleVote(card.value)}
-                      className="aspect-[2/3] rounded-sm border-2 transition-all flex flex-col items-center justify-center gap-1 hover:scale-105 cursor-pointer bg-transparent"
+                      disabled={!canVote}
+                      className="aspect-[2/3] rounded-sm border-2 transition-all flex flex-col items-center justify-center gap-1 hover:scale-105 cursor-pointer bg-transparent disabled:cursor-not-allowed"
                       style={{
                         borderColor: isSelected ? card.color : 'var(--card-border, #e2e8f0)',
                         backgroundColor: isSelected ? `${card.color}15` : 'transparent'