S5: WebSocket real-time — per-channel broadcast, auto-reconnect

Backend:
- AppState with per-channel broadcast::Sender map
- WS handler: auth via first message, keepalive pings, broadcast forwarding
- post_message broadcasts WsEvent::Message to all subscribers

Frontend:
- useChannelSocket hook: connects, auths, appends messages, auto-reconnects
- Removed 3s polling — WebSocket is primary, initial load via REST
- Deduplication on WS messages (sender also fetches after post)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/colony/src/hooks/useChannelSocket.ts

@@ -0,0 +1,61 @@
+import { useEffect, useRef, useCallback } from "react";
+import type { Message } from "@/types/Message";
+import { getCurrentUsername } from "@/api";
+
+interface WsMessageEvent {
+  event: "message";
+  data: Message;
+}
+
+interface WsConnectedEvent {
+  event: "connected";
+}
+
+type WsEvent = WsMessageEvent | WsConnectedEvent;
+
+export function useChannelSocket(
+  channelId: string | null,
+  onMessage: (msg: Message) => void,
+) {
+  const wsRef = useRef<WebSocket | null>(null);
+  const reconnectTimer = useRef<ReturnType<typeof setTimeout>>();
+
+  const connect = useCallback(() => {
+    if (!channelId) return;
+
+    const protocol = window.location.protocol === "https:" ? "wss:" : "ws:";
+    const host = window.location.host;
+    const ws = new WebSocket(`${protocol}//${host}/ws/${channelId}`);
+
+    ws.onopen = () => {
+      // Send auth message
+      ws.send(JSON.stringify({
+        type: "auth",
+        user: getCurrentUsername(),
+      }));
+    };
+
+    ws.onmessage = (e) => {
+      const event: WsEvent = JSON.parse(e.data);
+      if (event.event === "message") {
+        onMessage(event.data);
+      }
+    };
+
+    ws.onclose = () => {
+      // Reconnect after 3s
+      reconnectTimer.current = setTimeout(connect, 3000);
+    };
+
+    wsRef.current = ws;
+  }, [channelId, onMessage]);
+
+  useEffect(() => {
+    connect();
+    return () => {
+      clearTimeout(reconnectTimer.current);
+      wsRef.current?.close();
+      wsRef.current = null;
+    };
+  }, [connect]);
+}