fix: enforce single playing game and clean up stale shard monitors

Mark games as 'played' when shard detects game.ended or room_closed.
Stop old shard monitors before demoting previous playing games on new
game add or status change. Sync frontend playingGame state with the
games list on every refresh to prevent stale UI. Use terminate() for
probe connections to prevent shard connection leaks.

Made-with: Cursor

backend/routes/sessions.js

@@ -314,6 +314,14 @@ router.post('/:id/games', authenticateToken, (req, res) => {
       return res.status(404).json({ error: 'Game not found' });
     }
 
+    // Stop monitors for currently-playing games before demoting them
+    const previouslyPlaying = db.prepare(
+      'SELECT id FROM session_games WHERE session_id = ? AND status = ?'
+    ).all(req.params.id, 'playing');
+    for (const prev of previouslyPlaying) {
+      try { stopMonitor(req.params.id, prev.id); } catch (_) {}
+    }
+
     // Set all current 'playing' games to 'played' (except skipped ones)
     db.prepare(`
       UPDATE session_games 
@@ -590,8 +598,17 @@ router.patch('/:sessionId/games/:gameId/status', authenticateToken, (req, res) =
       return res.status(400).json({ error: 'Invalid status. Must be playing, played, or skipped' });
     }
 
-    // If setting to 'playing', first set all other games in session to 'played' or keep as 'skipped'
+    // If setting to 'playing', first stop monitors and demote other playing games
     if (status === 'playing') {
+      const previouslyPlaying = db.prepare(
+        'SELECT id FROM session_games WHERE session_id = ? AND status = ?'
+      ).all(sessionId, 'playing');
+      for (const prev of previouslyPlaying) {
+        if (String(prev.id) !== String(gameId)) {
+          try { stopMonitor(sessionId, prev.id); } catch (_) {}
+        }
+      }
+
       db.prepare(`
         UPDATE session_games 
         SET status = CASE