Fix poker:leave regression: move leave emit from PokerRoom to Room level

poker:leave was firing on every issue advance (PokerRoom unmount), causing
a race condition where participants were briefly removed and revealIfComplete
triggered after just 1 vote. Now poker:leave only emits when the user truly
leaves the room (Room component unmounts).

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

frontend/src/components/PokerRoom.jsx

@@ -80,7 +80,6 @@ export default function PokerRoom({ session, issue, user, onSaved }) {
     }
 
     return () => {
-      socket.emit('poker:leave', { sessionId: session.id });
       socket.off('poker:participants', onParticipants);
       socket.off('poker:vote-update', onVoteUpdate);
       socket.off('poker:revealed', onRevealed);

frontend/src/components/Room.jsx

@@ -1,5 +1,6 @@
-import { useCallback, useEffect, useRef, useState } from 'react';
+import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
 import { api } from '../services/api';
+import { getSocket } from '../services/socket';
 import PokerRoom from './PokerRoom';
 import DarkModeToggle from './DarkModeToggle';
 import AdfRenderer from './AdfRenderer';
@@ -13,6 +14,18 @@ export default function Room({ room, user, dark, toggleDark, onBack }) {
   const issuesRef = useRef([]);
 
   const pokerUser = { key: user.jiraAccountId, name: user.displayName };
+  const socket = useMemo(() => getSocket(), []);
+  const activeSessionIdRef = useRef(null);
+
+  // Emit poker:leave when the Room unmounts (user truly leaves the room)
+  useEffect(() => {
+    return () => {
+      const sessionId = activeSessionIdRef.current;
+      if (sessionId) {
+        socket.emit('poker:leave', { sessionId });
+      }
+    };
+  }, [socket]);
 
   useEffect(() => {
     loadIssues();
@@ -69,6 +82,7 @@ export default function Room({ room, user, dark, toggleDark, onBack }) {
 
   const activeSessionRef = useRef(null);
   activeSessionRef.current = activeSession;
+  activeSessionIdRef.current = activeSession?.session?.id || null;
 
   const advanceToNext = useCallback((estimate) => {
     if (!activeSessionRef.current) return;