Fix privacy redaction screen capture handling

[Kyle-Ye]

Summary

• Treat PrivacyRedactionViewModifier as a primitive multi-view modifier to avoid materializing a Body == Never body.
• Apply the screencaptureProhibited display-list property from the screen-capture redaction flag.
• Hide scrapeable content when either privacy redaction is active or screen capture is prohibited.

[augmentcode]

🤖 Augment PR Summary

Summary: Updates PrivacyRedactionViewModifier to be a primitive multi-view modifier and fixes screen-capture handling.
Behavior: Propagates .screencaptureProhibited from redaction reasons and hides scrapeable content when either privacy redaction or screen-capture prohibition is active.

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[augmentcode]

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 26.98%. Comparing base (90b3f69) to head (da330b9).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...UICore/Data/EnvironmentKeys/PrivacyRedaction.swift	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #874      +/-   ##
==========================================
- Coverage   26.98%   26.98%   -0.01%     
==========================================
  Files         678      678              
  Lines       47149    47149              
==========================================
- Hits        12724    12723       -1     
- Misses      34425    34426       +1     

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