feat: scaffold Svelte app with shared types and scale calculation

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.ts

@@ -0,0 +1,4 @@
+import { mount } from 'svelte';
+import App from './App.svelte';
+
+mount(App, { target: document.getElementById('app')! });