Add the web app manifest, icons and service worker via vite-plugin-pwa

vite-plugin-pwa runs in injectManifest mode over a minimal src/sw.ts that
caches the injected precache list on install. The manifest lives in
web/manifest.json (MealQuest, standalone at /, Grape theme over the page
background) with 192, 512 and maskable 512 PNG icons and a 180 px
apple-touch-icon, all generated from design/logos/logo_v1_2Oct2026.jpg by
web/scripts/generate-icons.py.

The plugin links the manifest and adds the registerSW.js script only in
production builds. src/pwa.test.ts builds and previews the app to assert
the shipped manifest, sw.js, icon sizes and registration, and checks that
the dev server registers nothing.

Maestro task: 58b74786-937a-45a5-850f-7913273beba2

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/vite.config.ts

@@ -1,10 +1,28 @@
 import { defineConfig } from 'vitest/config'
 import react from '@vitejs/plugin-react'
+import { VitePWA, type ManifestOptions } from 'vite-plugin-pwa'
+import manifest from './manifest.json' with { type: 'json' }
 
 const backend = 'http://localhost:8080'
 
 export default defineConfig({
-  plugins: [react()],
+  plugins: [
+    react(),
+    // The plugin writes manifest.webmanifest and sw.js, links the manifest
+    // from index.html and adds the registerSW.js script. It does both only
+    // in production builds: dev options stay off, so neither `vite` nor
+    // Vitest registers a service worker.
+    VitePWA({
+      strategies: 'injectManifest',
+      srcDir: 'src',
+      filename: 'sw.ts',
+      injectRegister: 'script',
+      // The web manifest lives in manifest.json: its theme and background
+      // colours are --color-accent and --color-bg from src/styles/tokens.css,
+      // and hex colours may not be written in TypeScript.
+      manifest: manifest as Partial<ManifestOptions>,
+    }),
+  ],
   server: {
     proxy: {
       '/api': backend,