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-network-app/node_modules/tailwindcss/stubs/tailwind.config.cjs

@@ -0,0 +1,2 @@
+/** @type {import('tailwindcss').Config} */
+module.exports = __CONFIG__