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/prettier.config.js

@@ -0,0 +1,19 @@
+module.exports = {
+  // These settings are duplicated in .editorconfig:
+  tabWidth: 2, // indent_size = 2
+  useTabs: false, // indent_style = space
+  endOfLine: 'lf', // end_of_line = lf
+  semi: false, // default: true
+  singleQuote: true, // default: false
+  printWidth: 100, // default: 80
+  trailingComma: 'es5',
+  bracketSpacing: true,
+  overrides: [
+    {
+      files: '*.js',
+      options: {
+        parser: 'flow',
+      },
+    },
+  ],
+}