Add comprehensive integration tests covering:
- TestIntegration_PathWithSlashes: nested paths work as distinct rooms
- TestIntegration_QueryStringIgnored: query strings stripped, same room
- TestIntegration_DefaultRoom: bare root path broadcast works
- TestIntegration_ClientDisconnectFromRoom: remaining clients communicate
- TestIntegration_ConcurrentRoomOperations: no races with rapid connect/disconnect
All tests pass with -race flag.
🤖 Assisted by the code-assist SOP
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