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/tailwindcss/colors.d.ts

@@ -0,0 +1,3 @@
+import type { DefaultColors } from './types/generated/colors'
+declare const colors: DefaultColors
+export = colors