Use custom headings for more notes tags

[janbrasna]

One-line summary

These have been reworded for about a decade since https://bugzil.la/1182225 as seen in Protocol version, but not Flare output.

Significant changes and points to review

Overrides titles from RNA tags for notes:

• "Known" → "Unresolved"
• "Community" → "Community Contributions"
• (+ removes one preexisting "Developer" special casing for equivalent tag default)

Extra flex shrink rule added to keep the icon the same size once headings start wrapping.

Keeping the current middle align to match wireframes:

Values taken from switch off conditions, just few lines down.

Issue / Bugzilla link

https://mozilla-hub.atlassian.net/browse/WT-930

Testing

http://localhost:8000/en-US/firefox/146.0/releasenotes/#known

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.16%. Comparing base (6efdf5f) to head (ee96529).
⚠️ Report is 31 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1168      +/-   ##
==========================================
+ Coverage   79.00%   79.16%   +0.15%     
==========================================
  Files         132      134       +2     
  Lines        8236     8323      +87     
==========================================
+ Hits         6507     6589      +82     
- Misses       1729     1734       +5     

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[maureenlholland]

r+ fixes unintentional naming regression from Flare26 styles