Fix sketch point constraint colours

[ksbharaj]

Summary

Render each sketch point using its own solver freedom rather than inheriting the colour of its owning segment.

For example, a constrained circle centre stays white even when the circle stroke is blue because another circle parameter remains free. This corrects the display; it does not change solver behaviour or constraint requirements.

Remove the now-unused point-owner field and cover free, fixed and conflicting point/segment colour combinations in renderer tests. The segment stroke retains its own constraint colour.

Scope

This PR is now point colours only, following the code owner's request to separate duplicate-name handling from constraint/DOF display changes. Instance selection is in #13882; execution performance/cancellation is in #13883, stacked on #13882. No region or segment-selection overlays are included.

The previously tested combined commit 70b856e29374d84ca2f0ca5707e0b2b427b551c9 is preserved on codex/sketch-visualization-tested-combined. Existing MCP/TTC pins still reference that complete build during review; this narrowed PR alone is not the full native dependency required by MCP #248.

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Project	Deployment	Actions	Updated
modeling-app	Ready	Preview	Sep 14, 2026 7:03pm UTC

[codspeed-hq]

Merging this PR will not alter performance

✅ 150 untouched benchmarks
⏩ 128 skipped benchmarks¹

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_{Comparing codex/plain-sketch-point-colors (4daa679) with main (081a5bf)²}

Footnotes

1. 128 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (2bdb7a0) during the generation of this report, so 081a5bf was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩