Add Apps page with local icons, favicon, and React Router navigation

- Move app links to dedicated /apps page with grouped icon tiles
- Download all icons locally to public/icons/ (no CDN dependency)
- Add favicon and replace header logo-mark with custom icon
- Fix icon names: synology, termix, docsight-light, dbgate (png)
- Add nav tabs in header for Dashboard/Apps routing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -15,6 +15,7 @@
     "express": "^4.19.2",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
+    "react-router-dom": "^6.24.0",
     "socket.io-client": "^4.8.3"
   },
   "devDependencies": {