fix(frontend): redirect root route to /files

The root route rendered the default SvelteKit placeholder page. Redirect /
to /files; the layout guard still sends unauthenticated users to /login.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/routes/+page.ts

@@ -0,0 +1,7 @@
+import { redirect } from '@sveltejs/kit';
+
+// The app has no content at the root; send users to the files view (the layout
+// guard redirects to /login first when unauthenticated).
+export const load = () => {
+	redirect(307, '/files');
+};