[Frontend] Implement PWA install prompt with offline-ready notification

[Penielka]

Description

The app already has a service worker for offline support. Add a customized PWA install flow: detect when the app is installable, show an in-app install banner (not just the browser default), and notify users when content is available offline. Use the beforeinstallprompt event.

Definition of Done

• Install prompt appears when PWA criteria are met (manifest, SW registered, HTTPS)
• Custom in-app install banner (not relying on browser default)
• "Install App" button in settings or header
• Install prompt is dismissible and does not reappear for 7 days after dismissal
• Offline-ready indicator in header when SW is active and content cached
• Post-install analytics event tracked
• Works on Chrome, Edge, and mobile Safari (iOS standalone mode)

Acceptance Criteria

1. Visit site on supported browser → install banner appears after 30s engagement
2. Dismiss banner → does not reappear for 7 days
3. Click install → PWA installed to home screen
4. Offline indicator shows when service worker has cached pages
5. Manifest icons are correct sizes for all platforms

Files to Modify

• frontend/src/components/PWA/InstallPrompt.tsx — enhance install UI
• New file: frontend/src/hooks/useInstallPrompt.ts — beforeinstallprompt logic
• frontend/src/components/PWA/OfflineIndicator.tsx — enhance offline indicator
• frontend/public/manifest.json — verify icons and fields
• frontend/src/app/layout.tsx — include install prompt component

[Achievers-sketch]

Experienced with React, Next.js, PWAs, and service workers. I can implement install prompts, offline indicators, analytics, and testing.

[gloskull]

Hello, I have 4 years of experience delivering solutions for projects like this, covering backend, frontend, and smart contract development. After carefully reviewing your requirements, I have a clear understanding of the task and am confident in my ability to deliver a clean, efficient, and thoroughly tested solution on time. I prioritize code quality, maintainability, and industry best practices throughout the development process.
My PR will be submitted in under 10hours.

[clintjeff2]

Hello, I have 6 years of experience working on tasks like this and handling similar challenges across backend, frontend, and smart-contract development. I have carefully read and fully understood the task requirements, and I am confident I can deliver a clean, efficient, and well-tested solution promptly. I always ensure high-quality implementation, maintainability, and adherence to best practices.

Pull request in 5 hours.