SCIX-684 fix: strip HTML tags from title in browser tab and meta tags

[thostetler]

Article titles containing HTML markup (sub, sup, i, b, math, etc.) were
being rendered with raw tags in browser tabs and social sharing meta tags
instead of plain text.

• Strip HTML from page title in AbsLayout using existing stripHtml utility
• Strip HTML from og:title, twitter:title, citation_title, dc.title in Metatags
• Preserve HTML in page body for MathJax rendering
• Add test coverage for HTML stripping in meta tags

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 71.8%. Comparing base (9678f94) to head (136af13).

Files with missing lines	Patch %	Lines
src/components/Metatags/Metatags.tsx	50.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #765     +/-   ##
========================================
- Coverage    71.8%   71.8%   -0.0%     
========================================
  Files         217     217             
  Lines       24485   24485             
  Branches     1402    1402             
========================================
- Hits        17575   17572      -3     
- Misses       6878    6881      +3     
  Partials       32      32             

Files with missing lines	Coverage Δ
src/components/Metatags/Metatags.tsx	93.0% <50.0%> (ø)

... and 2 files with indirect coverage changes

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