feat: Add presence heartbeat for Matrix online status

- matrix-gateway: POST /internal/matrix/presence/online endpoint
- usePresenceHeartbeat hook with activity tracking
- Auto away after 5 min inactivity
- Offline on page close/visibility change
- Integrated in MatrixChatRoom component

src/features/messenger/components/ChannelHeader.tsx

@@ -0,0 +1,43 @@
+import type { Channel } from '../types/messenger';
+
+interface Props {
+  channel: Channel;
+  isConnected?: boolean;
+}
+
+export function ChannelHeader({ channel, isConnected }: Props) {
+  return (
+    <div className="border-b border-white/10 p-4 bg-slate-900/80 backdrop-blur-sm">
+      <div className="flex items-center justify-between">
+        <div>
+          <h2 className="text-2xl font-bold text-white flex items-center gap-2">
+            {channel.visibility === 'public' && <span>#</span>}
+            {channel.visibility === 'private' && <span>🔒</span>}
+            {channel.name}
+          </h2>
+          {channel.topic && <p className="text-sm text-slate-400 mt-1">{channel.topic}</p>}
+        </div>
+        <div className="flex items-center gap-4">
+          {isConnected !== undefined && (
+            <div className="flex items-center gap-2">
+              <div
+                className={`
+                  w-2 h-2 rounded-full
+                  ${isConnected ? 'bg-green-500' : 'bg-red-500'}
+                `}
+              />
+              <span className="text-sm text-slate-400">
+                {isConnected ? 'Live' : 'Disconnected'}
+              </span>
+            </div>
+          )}
+          <div className="text-sm text-slate-400">{channel.matrix_room_id}</div>
+        </div>
+      </div>
+    </div>
+  );
+}
+
+
+
+