Fix durable workbook closing and release accessibility

[s243a]

Summary

• route every visible workbook close action through durable removal
• add an accessible final-workbook export reminder, Android Back handling, and a setting to restore the warning
• accept Android workbook imports exposed by cloud providers as generic binary files
• add screen-reader names and WCAG AA contrast improvements for compact header, Tour, output, and Run controls
• update the v1.3.2 What's New summary and translated catalogues
• advance the service-worker shell lock append-only

Verification

• full local release/offline/PWA and repository test suites passed
• git diff --check is clean
• fresh debug build tested on a Samsung Galaxy S24 (Android 16 / API 36):
  • Python/SymPy execution and rendered output
  • close persistence across a cold restart
  • final-workbook confirmation, focus handling, Android Back, and warning restoration
  • Android picker import of a .srwb file labeled as binary
  • English and Arabic release/accessibility layouts

This PR contains the exact commit tested on the phone: 2708c5799610f79f6078b55aca383fc498d6fe79.