fix: make vector ingestion canonical and atomic

backend/app/services/geojson_service.py

@@ -32,6 +32,7 @@ def parse_geojson_payload(raw_text: str | dict[str, Any]) -> dict[str, Any]:
     geometry_types: set[str] = set()
     geometries = []
     invalid_features = 0
+    z_dimension_features = 0
     polygon_area_m2: float | None = None
     crs_assumed = None
     for feature in features:
@@ -49,6 +50,8 @@ def parse_geojson_payload(raw_text: str | dict[str, Any]) -> dict[str, Any]:
             if not geom.is_valid:
                 invalid_features += 1
                 raise ValueError("Invalid geometry remains after repair")
+        if geom.has_z:
+            z_dimension_features += 1
         geometry_types.add(str(geom.geom_type))
         geometries.append(geom)
 
@@ -85,6 +88,8 @@ def parse_geojson_payload(raw_text: str | dict[str, Any]) -> dict[str, Any]:
         "bounds_json": bounds_json,
         "approximate_area_m2": polygon_area_m2,
         "invalid_features": invalid_features,
+        "z_dimension_feature_count": z_dimension_features,
+        "canonical_storage_dimension": "2D",
         "crs": crs,
         "crs_assumed": crs_assumed,
         "extracted_at": datetime.now(timezone.utc).isoformat(),