feat: support GeoJSON FeatureCollection tiles

[Komzpa]

Summary

• accept GeoJSON FeatureCollection tile payloads by normalizing wrapped Feature.geometry objects into Kothic's existing feature shape
• keep existing Kothic tile payloads unchanged
• normalize Leaflet JSON responses before Y-axis inversion so wrapped GeoJSON features can render and remain clickable

Fixes #67.

Validation

• npm test

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve normalized payload for subclass consumers

Rebinding data to Kothic.normalizeData(data) creates a new object for GeoJSON FeatureCollection inputs, but L.TileLayer.Kothic.Clickable._onKothicDataResponse (in dist/kothic-leaflet-clickable.js) still reads the original argument after calling the parent method. In that path, features remain type: "Feature" with nested geometry, so the clickable layer stores no point features and featureclick stops working for GeoJSON tiles. This regression occurs specifically when using the clickable layer with wrapped GeoJSON features.

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