refactor: migrate frontend from React to SvelteKit

web/src/routes/+layout.svelte

@@ -0,0 +1,27 @@
+<script lang="ts">
+import "./layout.css";
+import { Tooltip } from "bits-ui";
+import ThemeToggle from "$lib/components/ThemeToggle.svelte";
+
+let { children } = $props();
+</script>
+
+<svelte:head>
+  {@html `<script>
+    (function() {
+      const stored = localStorage.getItem("theme");
+      const prefersDark = window.matchMedia("(prefers-color-scheme: dark)").matches;
+      if (stored === "dark" || (!stored && prefersDark) || (stored === "system" && prefersDark)) {
+        document.documentElement.classList.add("dark");
+      }
+    })();
+  </script>`}
+</svelte:head>
+
+<Tooltip.Provider>
+  <div class="fixed top-5 right-5 z-50">
+    <ThemeToggle />
+  </div>
+
+  {@render children()}
+</Tooltip.Provider>