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/index.html

@@ -3,6 +3,8 @@
   <head>
     <meta charset="UTF-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <meta name="theme-color" content="#5a358c" />
+    <link rel="apple-touch-icon" href="/apple-touch-icon.png" />
     <title>MealQuest</title>
   </head>
   <body>