fix: register PWA service worker via virtual:pwa-register for offline support

@vite-pwa/sveltekit does not auto-inject SW registration into SSR HTML.
Add explicit registration via virtual:pwa-register in root layout onMount,
inject webmanifest link via virtual:pwa-info, disable SvelteKit's built-in
SW registration to avoid conflicts, and add required dependencies.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app.d.ts

@@ -1,3 +1,6 @@
+/// <reference types="vite-plugin-pwa/info" />
+/// <reference types="vite-plugin-pwa/vanillajs" />
+
 // See https://svelte.dev/docs/kit/types#app.d.ts
 // for information about these interfaces
 declare global {