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

node_modules/globals/index.d.ts

@@ -0,0 +1,6 @@
+import {ReadonlyDeep} from 'type-fest';
+import globalsJson = require('./globals.json');
+
+declare const globals: ReadonlyDeep<typeof globalsJson>;
+
+export = globals;