feat: add PWA support with manifest, icons, and theme color management

public/manifest.json

@@ -0,0 +1,17 @@
+{
+  "name": "Nezha Monitoring",
+  "short_name": "Nezha Monitoring",
+  "icons": [
+    {
+      "src": "/android-chrome-192x192.png",
+      "sizes": "192x192",
+      "type": "image/png",
+      "purpose": "any maskable"
+    }
+  ],
+  "theme_color": "hsl(0 0% 98%)",
+  "background_color": "hsl(0 0% 98%)",
+  "start_url": "/",
+  "display": "standalone",
+  "orientation": "portrait"
+}