Fixed ability to create wrong skeleton structure in constructor

[bsekachev]

Motivation and context

• Start adding new edge
• Click first point
• Do not click the second point, just click continue
• Edge added with target node undefined, when creating such element on canvas, UI fails

How has this been tested?

Checklist

• I submit my changes into the develop branch
• I have created a changelog fragment
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (see GitHub docs)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.

[Copilot]

Pull Request Overview

This PR fixes a bug in the skeleton configurator where users could create invalid skeleton structures by starting an edge but not completing it, which would cause UI crashes. The fix prevents context menu operations during incomplete edge creation and automatically cancels unfinished edges when submitting the configuration.

• Adds validation to prevent context menu actions when an edge is being created
• Implements automatic cleanup of incomplete edges during configuration submission
• Minor code formatting improvements for consistency

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
cvat-ui/src/components/labels-editor/skeleton-configurator.tsx	Adds edge validation logic and cleanup functionality to prevent invalid skeleton structures
changelog.d/20250902_105235_sekachev.bs_fixed_not_finished_skeleton.md	Documents the bug fix in the changelog

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[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

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.24%. Comparing base (2a579cd) to head (8c2cc64).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #9784      +/-   ##
===========================================
- Coverage    82.33%   82.24%   -0.09%     
===========================================
  Files          466      410      -56     
  Lines        48358    45311    -3047     
  Branches      4082     4082              
===========================================
- Hits         39814    37267    -2547     
+ Misses        8544     8044     -500     

Components	Coverage Δ
cvat-ui	77.26% <ø> (-0.01%)	⬇️
cvat-server	86.52% <ø> (+0.33%)	⬆️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.