feat(#49): return FK details in department and municipality serializers

- DepartmentSerializer adds country_detail (nested country object)
- MunicipalitySerializer adds department_detail and country_detail
- Writable FK id fields kept for create/update
- Move geography brief serializers to serializers/geography.py

tienda_ilusion/don_confiao/tests/test_provenance_api.py

@@ -219,6 +219,28 @@ class TestProvenanceCRUD(APITestCase, LoginMixin):
         self.assertEqual(data["municipality_detail"]["name"], "La Mesa")
         self.assertIn("products", data)
 
+    def test_department_serializer_includes_country_detail(self):
+        response = self.client.get(
+            f"/don_confiao/api/departments/{self.department.id}/"
+        )
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        data = response.json()
+        self.assertEqual(data["country"], self.country.id)
+        self.assertEqual(data["country_detail"]["name"], "Colombia")
+        self.assertEqual(data["country_detail"]["code"], "CO")
+
+    def test_municipality_serializer_includes_fk_details(self):
+        response = self.client.get(
+            f"/don_confiao/api/municipalities/{self.municipality.id}/"
+        )
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        data = response.json()
+        self.assertEqual(data["department"], self.department.id)
+        self.assertEqual(data["department_detail"]["name"], "Cundinamarca")
+        self.assertEqual(data["country"], self.country.id)
+        self.assertEqual(data["country_detail"]["name"], "Colombia")
+        self.assertEqual(data["country_detail"]["code"], "CO")
+
     def test_link_product_to_suppliers_via_product_api(self):
         product = Product.objects.create(name="Panela", price=5000)
         supplier2 = Supplier.objects.create(name="Proveedor 2")