feat: enable PWA offline support with service worker

Add SvelteKitPWA plugin to generate a service worker that precaches
static assets and uses NetworkFirst for API routes, enabling the app
to load offline. Generate pretzel emoji PWA icons and remove the old
static manifest (now generated by the plugin).

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

vite.config.ts

@@ -1,7 +1,42 @@
 import { sveltekit } from '@sveltejs/kit/vite';
+import { SvelteKitPWA } from '@vite-pwa/sveltekit';
 import tailwindcss from '@tailwindcss/vite';
 import { defineConfig } from 'vite';
 
 export default defineConfig({
-	plugins: [tailwindcss(), sveltekit()]
+	plugins: [
+		tailwindcss(),
+		sveltekit(),
+		SvelteKitPWA({
+			registerType: 'autoUpdate',
+			manifest: {
+				name: 'Crumbs by Bretzel',
+				short_name: 'Crumbs',
+				description: 'A self-hostable, offline-first note-taking app by Bretzel',
+				start_url: '/',
+				display: 'standalone',
+				background_color: '#202124',
+				theme_color: '#f59e0b',
+				icons: [
+					{ src: 'pwa-192x192.png', sizes: '192x192', type: 'image/png' },
+					{ src: 'pwa-512x512.png', sizes: '512x512', type: 'image/png' },
+					{ src: 'pwa-512x512.png', sizes: '512x512', type: 'image/png', purpose: 'maskable' }
+				]
+			},
+			workbox: {
+				globPatterns: ['client/**/*.{js,css,ico,png,svg,webp,woff,woff2}'],
+				navigateFallback: '/',
+				runtimeCaching: [
+					{
+						urlPattern: /^https?:\/\/.*\/api\//,
+						handler: 'NetworkFirst',
+						options: {
+							cacheName: 'api-cache',
+							expiration: { maxEntries: 50, maxAgeSeconds: 300 }
+						}
+					}
+				]
+			}
+		})
+	]
 });