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/plugin-missing.js

@@ -0,0 +1,19 @@
+"use strict";
+
+module.exports = function(it) {
+    const { pluginName, resolvePluginsRelativeTo, importerName } = it;
+
+    return `
+ESLint couldn't find the plugin "${pluginName}".
+
+(The package "${pluginName}" was not found when loaded as a Node module from the directory "${resolvePluginsRelativeTo}".)
+
+It's likely that the plugin isn't installed correctly. Try reinstalling by running the following:
+
+    npm install ${pluginName}@latest --save-dev
+
+The plugin "${pluginName}" was referenced from the config file in "${importerName}".
+
+If you still can't figure out the problem, please stop by https://eslint.org/chat/help to chat with the team.
+`.trimStart();
+};