feat(intl): support self-closing tags in rich-text formatter

[dangreen]

mapTags now recognizes self-closing tags (<br/>, <br />) and maps them via the tag handler with empty chunks, so line breaks and similar void elements can be expressed in rich-text messages. Unknown self-closing tags are still stripped as markup. Covered with unit tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.95%. Comparing base (25cd26d) to head (f47d44c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #185      +/-   ##
==========================================
+ Coverage   83.94%   83.95%   +0.01%     
==========================================
  Files         138      138              
  Lines        2983     2985       +2     
  Branches      563      564       +1     
==========================================
+ Hits         2504     2506       +2     
  Misses        340      340              
  Partials      139      139              

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.