feat(pwa): enable SvelteKit service worker registration

Story 4: Enable SvelteKit Service Worker Registration
- Enable serviceWorker.register: true in svelte.config.js
- SvelteKit now handles service worker registration automatically
- Service worker builds successfully as service-worker.mjs
- Build and preview work without conflicts
- Ready for comprehensive testing

Migration to native SvelteKit PWA implementation complete

Refs: docs/plans/MigrateToNativeSvelteKitPWA.md

svelte.config.js

@@ -9,7 +9,7 @@ const config = {
 	kit: { 
 		adapter: adapter(),
 		serviceWorker: {
-			register: false // Disable SvelteKit service worker - using @vite-pwa/sveltekit instead
+			register: true // Enable SvelteKit's native service worker registration
 		}
 	}
 };