Fix maintenance /assets 403 and remove vite-plugin-pwa

- nginx try_files: remove $uri/ so the Vite assets/ build directory
  doesn't shadow the /assets React route and trigger a 403
- Remove VitePWA plugin (leftover from scaffold, not needed for internal app)
- Strip PWA-specific nginx location blocks (manifest, sw.js, registerSW.js)

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

frontend/vite.config.ts

@@ -1,31 +1,7 @@
 import { defineConfig } from 'vite'
 import react from '@vitejs/plugin-react'
-import { VitePWA } from 'vite-plugin-pwa'
 
 export default defineConfig({
   base: '/maintenance/',
-  plugins: [
-    react(),
-    VitePWA({
-      registerType: 'autoUpdate',
-      manifest: {
-        name: 'Maintenance',
-        short_name: 'Maint.',
-        start_url: '/maintenance/',
-        scope: '/maintenance/',
-        display: 'standalone',
-        theme_color: '#b45309',
-        background_color: '#b45309',
-        icons: [
-          { src: '/maintenance/icons/icon-192.png', sizes: '192x192', type: 'image/png' },
-          { src: '/maintenance/icons/icon-512.png', sizes: '512x512', type: 'image/png' },
-        ],
-      },
-      workbox: {
-        navigateFallback: '/maintenance/index.html',
-        navigateFallbackDenylist: [/\/api\//],
-        globPatterns: ['**/*.{js,css,html,ico,png,svg}'],
-      },
-    }),
-  ],
+  plugins: [react()],
 })