fix: prevent FRACTIONAL colormap from being replaced on opacity change

[igoroctaviano]

Summary

Fix bug where FRACTIONAL segmentation colormaps get binarized (replaced with flat color LUT) when adjusting the opacity slider.

Root cause: SegmentItem.handleOpacityChange was always sending color along with opacity in the style options. For FRACTIONAL segments, this caused SlideViewer.handleSegmentStyleChange to create a new paletteColorLookupTable from that flat color, replacing the distinct colormap that was originally assigned.

Fix: handleOpacityChange now only sends opacity. Color changes are handled separately by handleColorChange, which is already hidden in the UI for FRACTIONAL segments.

Test plan

• Load a FRACTIONAL segmentation (e.g., https://viewer.imaging.datacommons.cancer.gov/slim/studies/2.25.213661963103110408605329613498871186883/series/1.2.826.0.1.3680043.10.511.3.51628462607277482021421207939845935)
• Adjust the opacity slider
• Verify the distinct colormap is preserved (not replaced with flat color)
• Verify BINARY segments still allow color changes via the color slider

Fixes #428

[deepsource-io]

DeepSource Code Review

We reviewed changes in a2912f1...d84e5e9 on this pull request. Below is the summary for the review, and you can see the individual issues we found as inline review comments.

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PR Report Card

Overall Grade

Security   Reliability   Complexity   Hygiene

Code Review Summary

Analyzer	Status	Updated (UTC)	Details
JavaScript		Aug 29, 2026 1:38p.m.	Review ↗

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

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