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/lines-and-columns/README.md

@@ -0,0 +1,33 @@
+# lines-and-columns
+
+Maps lines and columns to character offsets and back. This is useful for parsers
+and other text processors that deal in character ranges but process text with
+meaningful lines and columns.
+
+## Install
+
+```
+$ npm install [--save] lines-and-columns
+```
+
+## Usage
+
+```js
+import { LinesAndColumns } from 'lines-and-columns'
+
+const lines = new LinesAndColumns(
+  `table {
+  border: 0
+}`
+)
+
+lines.locationForIndex(9)
+// { line: 1, column: 1 }
+
+lines.indexForLocation({ line: 1, column: 2 })
+// 10
+```
+
+## License
+
+MIT