Fix hover labels rendering above shapes

[seveibar]

Summary

• Raise rect and polygon hover label boxes into a shared overlay layer so they render above overlapping graphics.
• Apply the same z-index to the hovered rect container to avoid stacking-context issues.
• Add a shared tooltip layer constant for the interactive graphics components.

Testing

• Unit tests passed across the graphics suite.
• Local build completed successfully.
• Interactive formatting checks passed.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
graphics-debug	Ready	Preview, Comment	Apr 26, 2026 0:40am

[tscircuitbot]

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PR Rating: ⭐⭐
Impact: Minor

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