Enable scripts in in-app message iframe for Safari compatibility

[franco-zalamena-iterable]

Summary

• Add allow-scripts to iframe sandbox attribute for in-app messages
• Remove Safari-specific restrictions that block click tracking

Test plan

• Test in-app message click tracking in Safari
• Test in-app message click tracking in Chrome
• Verify custom actions (action://...) work in Safari

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.87500% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 74.89%. Comparing base (190a168) to head (952ecd2).

Files with missing lines	Patch %	Lines
src/inapp/inapp.ts	96.87%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #574      +/-   ##
==========================================
+ Coverage   74.45%   74.89%   +0.44%     
==========================================
  Files          57       57              
  Lines        2736     2709      -27     
  Branches      798      786      -12     
==========================================
- Hits         2037     2029       -8     
+ Misses        698      679      -19     
  Partials        1        1              

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