feat: implement confidence score slider

[drduhe]

Issue #, if available: n/a

Summary

• Added confidence-based filtering for GeoJSON detections in the layer panel UI.
• Kept full detection loading intact; filtering now updates visibility in place by toggling entity display state.
• Added a global minimum-confidence slider (0.00–1.00) and per-layer display counts (shown / total) to make filter impact clear.

Implementation Notes

• Introduced featureConfidence utilities to:
  • extract confidence/score values from nested feature properties,
  • normalize values from either 0..1 or 0..100,
  • apply threshold filtering to loaded entities.
• Extended resource context with confidenceThreshold and setConfidenceThreshold, and applied filtering:
  • when threshold changes,
  • when feature collections are added,
  • when collection visibility is toggled.

Checklist

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• Performance impacts (if any) of the changes are evaluated and documented
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[devinglauner]

LGTM