Add dedicated integration tests verifying message isolation between rooms:
- TestIntegration_SameRoomBroadcast: two clients in /chat both receive
broadcast messages
- TestIntegration_CrossRoomIsolation: client in /room-a does not leak
messages to client in /room-b (verified via read deadline timeout)
- TestIntegration_MultipleRoomsSimultaneous: 3 rooms with 2 clients
each, messages stay within their room
- TestIntegration_RoomCleanup: verifies RoomCount() increases on
connect and decreases (room removed) on last client disconnect
- TestIntegration_RoomCleanup_MultipleClients: room persists while
any client remains connected
- TestIntegration_RoomCleanup_ConcurrentDisconnects: 5 rooms cleaned
up concurrently without races
Also introduces dialWSPath(t, server, path) helper for tests that
specify WebSocket paths directly with a leading slash.
All tests pass with -race flag.
🤖 Assisted by the code-assist SOP
