🐛 fix(effects): stabilize LOD effect culling

[24KaratAu]

What does this PR do?

Fixes visual popping of high-detail building effects during fly mode in dense city areas.

EffectsLayer.tsx already applied hysteresis for distance-based activation, but the maxActiveEffects capacity limit introduced a second instability source. Buildings near the active-set cutoff boundary continuously swapped positions during small camera movements, triggering rapid mount/unmount churn for ActiveBuildingEffects.

This change stabilizes the capacity-culling step by applying a small prioritization bias to already-active buildings:

const prioritizedDistSq = isActive
  ? Math.max(0,actualDistSq - hysteresisBiasSq)
  : actualDistSq;

This makes active effects slightly "stickier" so they remain mounted until meaningfully outdistanced by new candidates, reducing visible popping while preserving the existing rendering architecture and performance characteristics.

Related issue

Fixes #92

Screenshots

N/A (visual stabilization / reduced effect churn)

Checklist

• Tested locally
• No secrets or .env values committed
• npm run lint passes globally (repo currently contains unrelated pre-existing lint errors)

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds hysteresis bias when capping active effects to reduce LOD churn near the cutoff boundary by prioritizing already-active buildings.

Changes:

• Compute a hysteresis bias from farSq - nearSq
• Subtract bias from active buildings' squared distances when sorting for cap selection

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