feat(02-03): add CompletedToggle to show/hide completed tasks

- Create CompletedToggle component with checkbox UI
- Add showCompleted URL param to +page.server.ts load function
- Update +page.svelte to sync preferences with URL
- Toggle state persists in localStorage via preferences store
- Clicking toggle updates URL and invalidates data for server filter

src/routes/+page.server.ts

@@ -2,11 +2,13 @@ import type { PageServerLoad, Actions } from './$types';
 import { fail } from '@sveltejs/kit';
 import { entryRepository } from '$lib/server/db/repository';
 
-export const load: PageServerLoad = async () => {
-	const entries = entryRepository.getOrdered({ showCompleted: false });
+export const load: PageServerLoad = async ({ url }) => {
+	const showCompleted = url.searchParams.get('showCompleted') === 'true';
+	const entries = entryRepository.getOrdered({ showCompleted });
 
 	return {
-		entries
+		entries,
+		showCompleted
 	};
 };