Keep caption text readable with thick outlines

[jonoomph]

This fixes caption outlines covering the inside of letters, keeping text readable when a thick stroke is used.

• Rendering: Draw the outline before the text fill, while preserving captions without outlines.
• Regression coverage: Add a pixel-based check that reproduces the original defect.

Integrates #1107. Validated with caption/rendering tests and a short video export.

[jonoomph]

Merging 7 PRs from the community (Test caption rendering and Qt compatibility fixes)

[codecov]

Codecov Report

❌ Patch coverage is 98.90110% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 73.84%. Comparing base (983c847) to head (efb91fd).

Files with missing lines	Patch %	Lines
tests/Caption.cpp	97.67%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1128      +/-   ##
===========================================
+ Coverage    73.75%   73.84%   +0.08%     
===========================================
  Files          273      273              
  Lines        36794    36884      +90     
===========================================
+ Hits         27139    27236      +97     
+ Misses        9655     9648       -7     

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