feat(#49): add geolocation (latitude/longitude) to municipalities

- Municipality model with optional latitude/longitude decimal fields
- Municipality and brief serializers expose lat/lng (also in product_provenance of public/authenticated summaries for the Leaflet map)
- seed_geography endpoint reads lat/lng and updates existing municipalities on reseed (idempotent)
- TDD tests for model, serializers, summaries and seed

tienda_ilusion/don_confiao/api/provenance.py

@@ -92,7 +92,7 @@ class SeedGeographyView(APIView):
                 if created:
                     departments_created += 1
 
-            _, created = Municipality.objects.get_or_create(
+            municipality, created = Municipality.objects.get_or_create(
                 name=municipality_data["name"],
                 department=department,
                 defaults={"country": country},
@@ -100,6 +100,16 @@ class SeedGeographyView(APIView):
             if created:
                 municipalities_created += 1
 
+            latitude = municipality_data.get("latitude")
+            longitude = municipality_data.get("longitude")
+            if latitude is not None or longitude is not None:
+                municipality.country = country
+                if latitude is not None:
+                    municipality.latitude = latitude
+                if longitude is not None:
+                    municipality.longitude = longitude
+                municipality.save()
+
         return Response(
             {
                 "country": country.name,