refactor: move monitor page to index route and configure Tauri window

- Move monitor page content from /monitor to / (index route)
- Create placeholder monitor_.tsx route
- Remove Header component from root layout
- Configure Tauri window with transparent titlebar and dark background
- Enable macOS private API for window styling

apps/web/src-tauri/tauri.conf.json

@@ -16,9 +16,12 @@
         "width": 800,
         "height": 600,
         "resizable": true,
-        "fullscreen": false
+        "fullscreen": false,
+        "titleBarStyle": "Transparent",
+        "backgroundColor": "#0a0a0a"
       }
     ],
+    "macOSPrivateApi": true,
     "security": {
       "csp": null
     }