feat(mvp): phase 3 - authentication system

Implement local auth flow: login, registration, logout, JWT access/refresh
tokens in HTTP-only cookies, hooks.server.ts middleware, guest mode support,
Superforms + Zod validation, and reusable auth/authorize middleware.

src/routes/+layout.server.ts

@@ -0,0 +1,7 @@
+import type { LayoutServerLoad } from './$types.js';
+
+export const load: LayoutServerLoad = async ({ locals }) => {
+	return {
+		user: locals.user
+	};
+};