fix: correct extension marker dimensions for mobile/iOS rendering

[cyphercodes]

Issue

Fixes #7518

Problem

The extensionStart marker (used for implementation/realization arrows in class diagrams) had incorrect dimensions:

• markerWidth was 190 (should be 20)
• markerHeight was 240 (should be 28)

These typos caused the arrow markers to render incorrectly or not at all on mobile devices and iOS Safari.

Solution

Corrected the marker dimensions to match the extensionEnd marker and the margin variants:

• markerWidth: 20
• markerHeight: 28

Verification

This fix aligns the extensionStart marker with:

• extensionEnd marker (already had correct values)
• extensionStart-margin and extensionEnd-margin variants (already had correct values)
• Other similar markers in the same file

The path data (M 1,7 L18,13 V 1 Z) expects a viewBox of approximately 20x14, so markerWidth=20 and markerHeight=28 are appropriate values.

[changeset-bot]

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Latest commit: b804f7e

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commit: b804f7e

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 3.34%. Comparing base (e9d4c11) to head (b804f7e).

Files with missing lines	Patch %	Lines
...d/src/rendering-util/rendering-elements/markers.js	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #7538      +/-   ##
==========================================
- Coverage     3.34%   3.34%   -0.01%     
==========================================
  Files          524     525       +1     
  Lines        55256   55267      +11     
  Branches       795     795              
==========================================
  Hits          1850    1850              
- Misses       53406   53417      +11     

Flag	Coverage Δ
unit	3.34% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...d/src/rendering-util/rendering-elements/markers.js	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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