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/dlv/index.js

@@ -0,0 +1,7 @@
+export default function dlv(obj, key, def, p, undef) {
+	key = key.split ? key.split('.') : key;
+	for (p = 0; p < key.length; p++) {
+		obj = obj ? obj[key[p]] : undef;
+	}
+	return obj === undef ? def : obj;
+}