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/tailwindcss/nesting/index.d.ts

@@ -0,0 +1,4 @@
+import type { AcceptedPlugin, PluginCreator } from 'postcss'
+
+declare const plugin: PluginCreator<AcceptedPlugin | string | void>
+export = plugin

node_modules/tailwindcss/nesting/index.js

@@ -0,0 +1,2 @@
+let nesting = require('../lib/postcss-plugins/nesting')
+module.exports = (nesting.__esModule ? nesting : { default: nesting }).default