TYPO3 v13 adjustments

[maikschneider]

This PR makes several adjustments for usage in TYPO3 v13.3.0:

• add separate template for v13
• dark mode adjustments
• replace btn-outline-primary with btn-default
• re-activate v13 workflow tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.51%. Comparing base (c0103e7) to head (82c1795).
Report is 25 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #38      +/-   ##
==========================================
+ Coverage   88.46%   88.51%   +0.05%     
==========================================
  Files           6        6              
  Lines         208      209       +1     
==========================================
+ Hits          184      185       +1     
  Misses         24       24              

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