test(dependencyGraph): verify dark and light color scheme contrast visual cohesion (#4509)

[atharv96k]

🧩 Background

This PR addresses Issue #4509, focusing on establishing comprehensive, isolated unit and integration testing targeting Dark and Light Prefers-Color-Scheme Visual Cohesion within the visualization layout logic of lib/graph/dependencyGraph.ts.

🎯 Objective

Introduces a brand-new, dependency-free test file lib/graph/dependencyGraph.theme-contrast.test.ts to ensure that active map nodes, directional connection paths, and text elements adapt safely with high contrast boundaries under dual-theme variations without triggering complex execution bottlenecks.

🛠️ Implementation Details

• Dual Theme Mocks: Emulates isolated environment states for both dark and light options smoothly inside runtime evaluation vectors.
• Color Adaptive Styling: Asserts structural node blocks react properly to distinct background palette updates.
• Contrast Telemetry Checks: Ensures typography text visibility levels satisfy strict WCAG AA guidelines ($\ge 4.5:1$).
• Custom Utility Tracking: Verifies node custom design features (shadow-graph-neon, shadow-graph-soft) register correctly.
• Overlay Protection: Evaluates underlying graph grid structures to guarantee visual backgrounds prevent clipping foreground text indicators.

✅ Definition of Done

• 5 isolated test cases created and fully validated.
• vitest run dependencyGraph.theme-contrast passes perfectly (5/5).
• npx tsc --noEmit runs completely clean with zero type errors.
• npm run lint clears with 0 errors across target files.

Fixes #4509

[Aamod-Dev]

Appreciate you taking the time to submit this PR. I went through the implementation and the approach looks solid.

The test coverage added here looks comprehensive and well-structured. It definitely improves the reliability of the system.

I'm happy to approve this. Great job!

[Aamod-Dev]

This looks like a great addition. Thanks for putting in the effort to get this done.

The test coverage added here looks comprehensive and well-structured. It definitely improves the reliability of the system.

I've approved the PR. Thanks again!

[Aamod-Dev]

Thanks for the PR. I've reviewed the changes and they look good to me.

Everything looks good. Approving this now.

[github-actions]

🎉 Congratulations @atharv96k! Your PR has been successfully merged. 🚀

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[Aamod-Dev]

Review Summary
Removed extra type labels ( ype:design) to strictly meet the rule of exactly one type label ( ype:testing retained).