Add unplugin-icons & use Mingcute icons

Register unplugin-icons (Icons Vite plugin) in astro.config and add unplugin-icons + @iconify-json/mingcute to devDependencies. Replace inline SVGs in ThemeSwitcher.vue with MingcuteSunLine / MingcuteMoonLine icon components imported from ~icons, and add unplugin-icons types to tsconfig. Also simplify VSCode formatter setting and update package.json accordingly.

tsconfig.json

@@ -4,6 +4,7 @@
   "exclude": ["dist"],
   "compilerOptions": {
     "strictNullChecks": true,
-    "jsx": "preserve"
+    "jsx": "preserve",
+    "types": ["unplugin-icons/types/vue"]
   }
 }