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/json-stable-stringify-without-jsonify/package.json

@@ -0,0 +1,43 @@
+{
+  "name": "json-stable-stringify-without-jsonify",
+  "version": "1.0.1",
+  "description": "deterministic JSON.stringify() with custom sorting to get deterministic hashes from stringified results, with no public domain dependencies",
+  "main": "index.js",
+  "dependencies": {
+  },
+  "devDependencies": {
+    "tape": "~1.0.4"
+  },
+  "scripts": {
+    "test": "tape test/*.js"
+  },
+  "testling": {
+    "files": "test/*.js",
+    "browsers": [
+      "ie/8..latest",
+      "ff/5", "ff/latest",
+      "chrome/15", "chrome/latest",
+      "safari/latest",
+      "opera/latest"
+    ]
+  },
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/samn/json-stable-stringify.git"
+  },
+  "homepage": "https://github.com/samn/json-stable-stringify",
+  "keywords": [
+    "json",
+    "stringify",
+    "deterministic",
+    "hash",
+    "sort",
+    "stable"
+  ],
+  "author": {
+    "name": "James Halliday",
+    "email": "mail@substack.net",
+    "url": "http://substack.net"
+  },
+  "license": "MIT"
+}