feat(frontend): serve as SPA via adapter-static

frontend/svelte.config.js

@@ -1,12 +1,9 @@
-import adapter from '@sveltejs/adapter-auto';
+import adapter from '@sveltejs/adapter-static';
 
 /** @type {import('@sveltejs/kit').Config} */
 const config = {
     kit: {
-        // adapter-auto only supports some environments, see https://svelte.dev/docs/kit/adapter-auto for a list.
-        // If your environment is not supported, or you settled on a specific environment, switch out the adapter.
-        // See https://svelte.dev/docs/kit/adapters for more information about adapters.
-        adapter: adapter()
+        adapter: adapter({ fallback: 'index.html' })
     }
 };