fix: add missing PWA icons to resolve 404 errors in manifest

[Rakshita006]

📝 PR Description

Closes #73

The PWA manifest (manifest.json) referenced three icon files that did
not exist in the repository, causing 404 errors in the browser console
on every page load:

• GET /icons/icon-72x72.png 404
• GET /icons/icon-192x192.png 404
• GET /icons/icon-512x512.png 404

This also caused the PWA install prompt to fail and broke the app's
installability as a Progressive Web App.

Fix: Created the missing /icons/ directory and generated all three
required PNG icons using the existing app logo from the CDN, resized to
the correct dimensions using sharp.

🎯 GSSoC Points Target

• Difficulty: level:critical
• Quality: quality:exceptional
• Labels Requested: gssoc:approved, level:critical, type:bug

💎 Quality Checklist

• PWA: Manifest icons now resolve correctly
• Performance: Icons properly sized (72x72, 192x192, 512x512)
• Code Quality: No JS changes, clean isolated fix

📸 Screenshots / Video

Before: Console showed 3 icon 404 errors on every page load
After: Icon errors completely gone from console ✅

🧪 Testing Done

1. Ran npm run serve
2. Opened Chrome DevTools Console
3. Confirmed all 3 icon 404 errors are resolved
4. Verified remaining console messages are unrelated expected issues