Expand channel detection from JS/TS to 8 languages

Extend extract_channels.c from JS/TS/TSX-only to Python, Go, Java/Kotlin,
C#, Ruby, Elixir, and Rust with language-specific extractors:

- JS/TS: add Kafka (producer.send/consumer.subscribe), RabbitMQ
  (channel.publish/consume) on top of existing Socket.IO + EventEmitter
- Python: python-socketio (sio.emit/@sio.on), Django Channels
  (channel_layer.send/group_send), FastAPI WebSocket, kafka-python
- Go: gorilla/nhooyr websocket (WriteMessage/ReadMessage/WriteJSON/ReadJSON)
- Java/Kotlin: JSR 356 WebSocket (@OnMessage/@serverendpoint),
  Spring STOMP (convertAndSend/@MessageMapping)
- C#: SignalR (Clients.All.SendAsync/Hub.On)
- Ruby: ActionCable (broadcast/stream_from)
- Elixir: Phoenix.PubSub (broadcast/subscribe), Phoenix.Channel
  (push/handle_in)
- Rust: tokio-tungstenite (sink.send/stream.next)

Refactored entry point from language gate to switch dispatch. Python
direction classification uses table-driven lookup for linter compliance.

Author: DeusData