SDK-31 Fix full-position IAM safe area handling

[sumeruchat]

What

Fixes full-position in-app messages not respecting safe area insets, causing content to be hidden behind notch/Dynamic Island, status bar, and home indicator.

Changes

• Added set(contentInset:) to WebViewProtocol for scrollView content inset control
• Applied safe area insets to scrollView content for full-position IAMs in resizeWebView
• WebView still covers full screen (edge-to-edge background) but content is padded within safe areas

Impact

• Breaking changes: None
• Behavior change: Full-position IAMs now pad content within safe areas automatically
• Other positions: Top, bottom, center positions unaffected

Testing

How to test:

1. Create an in-app message with full position (top=0%, bottom=0%)
2. Display on device with notch/Dynamic Island (iPhone X or newer)
3. Verify content is visible and not hidden behind system UI
4. Verify background still covers full screen edge-to-edge
5. Test top/bottom/center positions still work correctly

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.75%. Comparing base (e5176d4) to head (cf5814f).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...k/Internal/IterableHtmlMessageViewController.swift	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #996      +/-   ##
==========================================
+ Coverage   69.73%   69.75%   +0.02%     
==========================================
  Files         111      111              
  Lines        8983     8993      +10     
==========================================
+ Hits         6264     6273       +9     
- Misses       2719     2720       +1     

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