Mobile PWA support (offline, installable)

[tacheraSasi]

Feature: Mobile PWA Support

Add a manifest.json and service worker so the serve page works offline and is installable.

Details

• Generate a manifest.json with app name, icons, theme colors
• Icons are already embedded in assets/icons/
• Add a service worker that caches:
  • The CSS and JS assets
  • Previously visited markdown pages
• Support "Add to Home Screen" on mobile browsers
• Show an install prompt banner
• Cache invalidation on content changes
• Works alongside the existing auto-reload mechanism

Why

Makes mdcli-served docs accessible offline on mobile devices, great for documentation that needs to be available in the field.