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/lodash.merge/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "lodash.merge",
+  "version": "4.6.2",
+  "description": "The Lodash method `_.merge` exported as a module.",
+  "homepage": "https://lodash.com/",
+  "icon": "https://lodash.com/icon.svg",
+  "license": "MIT",
+  "keywords": "lodash-modularized, merge",
+  "author": "John-David Dalton <john.david.dalton@gmail.com>",
+  "contributors": [
+    "John-David Dalton <john.david.dalton@gmail.com>",
+    "Mathias Bynens <mathias@qiwi.be>"
+  ],
+  "repository": "lodash/lodash",
+  "scripts": { "test": "echo \"See https://travis-ci.org/lodash/lodash-cli for testing details.\"" }
+}