Add missing HTML5 block elements to HtmlToDjot

[dereuromark]

Summary

• Add support for HTML5 semantic block elements that were missing from HtmlToDjot:

  • address - contact information
  • details - disclosure widget
  • dialog - dialog box
  • fieldset - form group
  • form - form container
  • hgroup - heading group
  • menu - menu container
  • search - search section (HTML5.2)

• These elements are now properly recognized in both:

  • The $blockElements array (for breaking implicit paragraphs)
  • The match statement (for processing as block containers)

Test plan

• Added 10 new test cases for HTML5 block elements
• Tests verify content extraction works correctly
• Tests verify block elements break implicit paragraphs
• All 79 HtmlToDjot tests pass
• PHPStan Level 9 passes

Closes #58

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.48%. Comparing base (61ee4cd) to head (107a1ea).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #64      +/-   ##
============================================
+ Coverage     93.42%   93.48%   +0.05%     
  Complexity     1956     1956              
============================================
  Files            74       74              
  Lines          5246     5247       +1     
============================================
+ Hits           4901     4905       +4     
+ Misses          345      342       -3     

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