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/escape-string-regexp/index.js

@@ -0,0 +1,13 @@
+'use strict';
+
+module.exports = string => {
+	if (typeof string !== 'string') {
+		throw new TypeError('Expected a string');
+	}
+
+	// Escape characters with special meaning either inside or outside character sets.
+	// Use a simple backslash escape when it’s always valid, and a \unnnn escape when the simpler form would be disallowed by Unicode patterns’ stricter grammar.
+	return string
+		.replace(/[|\\{}()[\]^$+*?.]/g, '\\$&')
+		.replace(/-/g, '\\x2d');
+};