Add localStorage feature detection to prevent throws in restricted environments

[franco-zalamena-iterable]

Summary

• Add safe localStorage wrapper with feature detection
• Falls back to in-memory storage when localStorage is unavailable
• Prevents throws in mobile webviews and iOS Safari private browsing

Test plan

• Test in normal browser (localStorage works)
• Test in private browsing mode
• Verify setUserId and setEmail work in both scenarios

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

❌ Patch coverage is 76.19048% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.12%. Comparing base (190a168) to head (d88b9b7).

Files with missing lines	Patch %	Lines
src/utils/safeStorage.ts	55.31%	18 Missing and 3 partials ⚠️
src/utils/functions.ts	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #573      +/-   ##
==========================================
- Coverage   74.45%   74.12%   -0.33%     
==========================================
  Files          57       58       +1     
  Lines        2736     2787      +51     
  Branches      798      826      +28     
==========================================
+ Hits         2037     2066      +29     
+ Misses        698      677      -21     
- Partials        1       44      +43     

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