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/slash/index.d.ts

@@ -0,0 +1,25 @@
+/**
+Convert Windows backslash paths to slash paths: `foo\\bar` ➔ `foo/bar`.
+
+[Forward-slash paths can be used in Windows](http://superuser.com/a/176395/6877) as long as they're not extended-length paths and don't contain any non-ascii characters.
+
+@param path - A Windows backslash path.
+@returns A path with forward slashes.
+
+@example
+```
+import * as path from 'path';
+import slash = require('slash');
+
+const string = path.join('foo', 'bar');
+// Unix    => foo/bar
+// Windows => foo\\bar
+
+slash(string);
+// Unix    => foo/bar
+// Windows => foo/bar
+```
+*/
+declare function slash(path: string): string;
+
+export = slash;