Add support for GFM admonition

[anonymaew]

Summary

Add support for GitHub Flavored Markdown admonitions, which was added in v0.5. The "kind" should be left untouched while their body content is translated.

Changes

• Enable ENABLE_GFM option so GFM alerts parse as BlockQuote(Some(BlockQuoteKind))¹ events.
• Grouping: The alert marker is treated as a Skip group; the body text is grouped as Translate groups (paragraphs inside the blockquote).
• Translation: Translated body content is re-wrapped in a BlockQuote event to preserve the GFM structure. Untranslatable alerts pass through unchanged.

Result

	Before	After
Rendered

Footnotes

1. https://docs.rs/pulldown-cmark/latest/pulldown_cmark/enum.BlockQuoteKind.html ↩

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.43750% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.91%. Comparing base (9b96374) to head (4902643).
⚠️ Report is 45 commits behind head on main.

Files with missing lines	Patch %	Lines
i18n-helpers/src/lib.rs	98.14%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #307      +/-   ##
==========================================
- Coverage   86.05%   85.91%   -0.14%     
==========================================
  Files          17       17              
  Lines        3750     3429     -321     
  Branches     3750     3429     -321     
==========================================
- Hits         3227     2946     -281     
+ Misses        419      380      -39     
+ Partials      104      103       -1     

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