Add public GeoJSON features API and load public 3D objects on maps.

Expose GET /v1/features/public (optional kind filter) and update Leaflet/MapLibre demos to render all public 3D assets globally, while still merging owner collections after login.

Made-with: Cursor

internal/store/memory.go

@@ -195,6 +195,16 @@ func (s *MemoryStore) ListFeaturesByCollection(collectionID string) []Feature {
 	return result
 }
 
+func (s *MemoryStore) ListFeaturesAll() []Feature {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	result := make([]Feature, 0, len(s.features))
+	for _, f := range s.features {
+		result = append(result, f)
+	}
+	return result
+}
+
 func (s *MemoryStore) GetFeature(featureID string) (Feature, error) {
 	s.mu.RLock()
 	defer s.mu.RUnlock()