Harden PWA icon generation and validation

[aliorhun]

Summary

Replaces the useful parts of the closed/conflicted PR #7 with a clean change set on top of the current main.

Included

• remove the old committed binary PWA icon files
• generate deterministic 192×192 and 512×512 PNG icons during npm run build
• keep the current content-hashed application bundle architecture unchanged
• use the generated local 192×192 icon as the browser favicon and Apple touch icon
• remove the large embedded base64 favicon data from index.html
• add mobile-web-app-capable
• extend offline/PWA verification to validate:
  • PNG signature
  • expected dimensions
  • every PNG chunk CRC
  • local favicon metadata
  • absence of embedded base64 favicon data

Explicitly not carried over from PR #7

The old fixed-name ./app.js / ./app.css deployment logic is not restored. The current assets/app-<hash>.js and assets/app-<hash>.css build remains intact.