feat: implement progressive web app support with offline capabilities

Add complete PWA implementation including service worker registration,
offline support, and installation prompts:

- Add vite-plugin-pwa and workbox-window dependencies for PWA tooling
- Configure VitePWA plugin with web app manifest and app metadata
- Set up Workbox caching strategies for API endpoints and CDN assets
- Implement service worker auto-update with user-triggered refresh
- Create usePWAInstall hook to handle beforeinstallprompt events
- Create useOnlineStatus hook for monitoring network connectivity
- Add InstallPrompt component with haptic feedback integration
- Add OfflineBanner component to notify users of offline status
- Configure PWA icons and assets (64x64, 192x192, 512x512 variants)
- Add TypeScript type declarations for virtual PWA register module
- Integrate PWA components and service worker into App.tsx and main.tsx
- Add PWA meta tags and viewport configuration to index.html

web/src/components/InstallPrompt.tsx

@@ -0,0 +1,40 @@
+import { usePWAInstall } from '@/hooks/usePWAInstall'
+import { usePlatform } from '@/hooks/usePlatform'
+
+export function InstallPrompt() {
+    const { canInstall, promptInstall, isStandalone } = usePWAInstall()
+    const { isTelegram, haptic } = usePlatform()
+
+    if (isTelegram || isStandalone || !canInstall) {
+        return null
+    }
+
+    const handleInstall = async () => {
+        haptic.impact('light')
+        const success = await promptInstall()
+        if (success) {
+            haptic.notification('success')
+        }
+    }
+
+    return (
+        <div className="fixed bottom-4 left-4 right-4 bg-[var(--app-secondary-bg)] border border-[var(--app-border)] rounded-lg p-4 shadow-lg z-50">
+            <div className="flex items-center justify-between gap-3">
+                <div className="flex-1 min-w-0">
+                    <p className="text-sm font-medium text-[var(--app-fg)]">
+                        Install Happy App
+                    </p>
+                    <p className="text-xs text-[var(--app-hint)] mt-0.5">
+                        Add to home screen for the best experience
+                    </p>
+                </div>
+                <button
+                    onClick={handleInstall}
+                    className="shrink-0 px-4 py-2 bg-[var(--app-button)] text-[var(--app-button-text)] rounded-lg text-sm font-medium active:opacity-80"
+                >
+                    Install
+                </button>
+            </div>
+        </div>
+    )
+}

web/src/components/OfflineBanner.tsx

@@ -0,0 +1,15 @@
+import { useOnlineStatus } from '@/hooks/useOnlineStatus'
+
+export function OfflineBanner() {
+    const isOnline = useOnlineStatus()
+
+    if (isOnline) {
+        return null
+    }
+
+    return (
+        <div className="fixed top-0 left-0 right-0 bg-amber-500 text-white text-center py-2 text-sm font-medium z-50">
+            You're offline. Some features may be unavailable.
+        </div>
+    )
+}