feat: PWA support — installable on all platforms

- Add vite-plugin-pwa with autoUpdate service worker
- Generate SVG + PNG icons (192, 512, apple-touch-icon, favicon)
- Web app manifest with standalone display mode
- Workbox caching: precache assets, cache Google Fonts, NetworkFirst for API
- Apple mobile web app meta tags for iOS home screen

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

frontend/vite.config.ts

@@ -1,9 +1,54 @@
 import { defineConfig } from 'vite'
 import vue from '@vitejs/plugin-vue'
 import tailwindcss from '@tailwindcss/vite'
+import { VitePWA } from 'vite-plugin-pwa'
 
 export default defineConfig({
-  plugins: [vue(), tailwindcss()],
+  plugins: [
+    vue(),
+    tailwindcss(),
+    VitePWA({
+      registerType: 'autoUpdate',
+      includeAssets: ['icon.svg'],
+      manifest: {
+        name: 'BOTFIGHTS',
+        short_name: 'BOTFIGHTS',
+        description: 'A safe place to hash it out',
+        theme_color: '#0a0a0a',
+        background_color: '#0a0a0a',
+        display: 'standalone',
+        orientation: 'any',
+        start_url: '/',
+        icons: [
+          { src: '/icon.svg', sizes: 'any', type: 'image/svg+xml', purpose: 'any' },
+          { src: '/icon-192.png', sizes: '192x192', type: 'image/png' },
+          { src: '/icon-512.png', sizes: '512x512', type: 'image/png' },
+          { src: '/icon-512.png', sizes: '512x512', type: 'image/png', purpose: 'maskable' },
+        ],
+      },
+      workbox: {
+        globPatterns: ['**/*.{js,css,html,svg,png,woff,woff2}'],
+        navigateFallback: '/index.html',
+        runtimeCaching: [
+          {
+            urlPattern: /^https:\/\/fonts\.googleapis\.com\/.*/i,
+            handler: 'CacheFirst',
+            options: { cacheName: 'google-fonts-css', expiration: { maxEntries: 10, maxAgeSeconds: 60 * 60 * 24 * 365 } },
+          },
+          {
+            urlPattern: /^https:\/\/fonts\.gstatic\.com\/.*/i,
+            handler: 'CacheFirst',
+            options: { cacheName: 'google-fonts-webfont', expiration: { maxEntries: 30, maxAgeSeconds: 60 * 60 * 24 * 365 } },
+          },
+          {
+            urlPattern: /\/api\/.*/i,
+            handler: 'NetworkFirst',
+            options: { cacheName: 'api-cache', expiration: { maxEntries: 50, maxAgeSeconds: 60 * 5 } },
+          },
+        ],
+      },
+    }),
+  ],
   server: {
     port: 9101,
     proxy: {