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/eslint/messages/file-not-found.js

@@ -0,0 +1,10 @@
+"use strict";
+
+module.exports = function(it) {
+    const { pattern, globDisabled } = it;
+
+    return `
+No files matching the pattern "${pattern}"${globDisabled ? " (with disabling globs)" : ""} were found.
+Please check for typing mistakes in the pattern.
+`.trimStart();
+};