Increase maximum popup width from 750px to 800px

[olsh]

Summary

• Increases the maximum allowed popup width from 750px to 800px (the browser-enforced maximum)
• Updates both popupWidth and expandedPopupWidth settings

Browser Limits Research

All major browsers enforce a hardcoded 800x600px maximum for extension popups:

• Chrome/Edge: 800px max (Chromium source: kMaxSize = {800, 600})
• Firefox: 800px max (since Firefox 60)

Changes

• src/scripts/core.js: Updated maxValue in both popupWidth and expandedPopupWidth getters
• src/options.html: Updated max attribute on both width input fields

Closes #240

[NinjaMilez]

Thank you for implementing my suggestion. :D