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/fast-glob/out/utils/array.d.ts

@@ -0,0 +1,2 @@
+export declare function flatten<T>(items: T[][]): T[];
+export declare function splitWhen<T>(items: T[], predicate: (item: T) => boolean): T[][];