feat(ui): add mode-watcher (dark/light mode)

src/routes/+layout.svelte

@@ -1,6 +1,8 @@
 <script lang="ts">
-	import '../app.css';
+	import "../app.css";
+	import { ModeWatcher } from "mode-watcher";
 	let { children } = $props();
 </script>
 
+<ModeWatcher />
 {@render children()}