Add PWA installation prompt for native app-like experience on mobile

[jpdevhub]

Since FreshScan is primarily used by users on their phones in high-humidity fish markets, having a native app experience is critical. The app is already partially PWA-ready, but we need to actively prompt mobile users to 'Install' or 'Add to Home Screen' when they visit the site.

Acceptance Criteria:

• Detect if the user is on a mobile browser and hasn't installed the app.
• Display a sleek, brutalist UI popup prompting them to 'Install FreshScan AI'.
• Hook into the browser's beforeinstallprompt event to trigger the installation.

[the-madhankumar]

I’d like to contribute to this issue under SSOC 2026. Please assign it to me; I’ll implement mobile install detection and a brutalist PWA install prompt using the beforeinstallprompt event to enhance the native app experience for FreshScan AI users.

[jpdevhub]

go ahead