Fix circular reference recursion in JSON serialization

Dataclass models have parent back-references (TrackLayout→Circuit→
Locality→Country) causing infinite recursion in dataclasses.asdict().
Add to_dict() methods that exclude parent refs, use them in API endpoints.

cdn-api.py

@@ -67,7 +67,7 @@ async def root():
 async def get_countries():
     """Get list of all available countries with their slugs"""
     return {
-        "countries": circuit_service.get_countries_list()
+        "countries": [c.to_dict() for c in circuit_service.get_countries_list()]
     }
 
 @app.get("/circuits/{country_slug}")
@@ -76,7 +76,7 @@ async def get_cities(country_slug: str):
     cities = circuit_service.get_localities_list(country_slug)
     if not cities:
         raise HTTPException(status_code=404, detail="Country not found")
-    return {"cities": cities}
+    return {"cities": [c.to_dict() for c in cities]}
 
 @app.get("/circuits/{country_slug}/{city_slug}")
 async def get_circuits(country_slug: str, city_slug: str):
@@ -84,7 +84,7 @@ async def get_circuits(country_slug: str, city_slug: str):
     circuits = circuit_service.get_circuits_list(country_slug, city_slug)
     if not circuits:
         raise HTTPException(status_code=404, detail="City not found")
-    return {"circuits": circuits}
+    return {"circuits": [c.to_dict() for c in circuits]}
 
 @app.get("/circuits/{country_slug}/{city_slug}/{circuit_slug}")
 async def get_circuit_details(country_slug: str, city_slug: str, circuit_slug: str):
@@ -92,7 +92,7 @@ async def get_circuit_details(country_slug: str, city_slug: str, circuit_slug: s
     circuit_details = circuit_service.get_circuit_details(country_slug, city_slug, circuit_slug)
     if not circuit_details:
         raise HTTPException(status_code=404, detail="Circuit not found")
-    return circuit_details
+    return circuit_details.to_dict()
 
 @app.get("/circuits/{country_slug}/{city_slug}/{circuit_slug}/layout/{layout_slug}")
 async def get_layout_details(country_slug: str, city_slug: str, circuit_slug: str, layout_slug: str):
@@ -100,7 +100,7 @@ async def get_layout_details(country_slug: str, city_slug: str, circuit_slug: st
     layout_details = circuit_service.get_layout_details(country_slug, city_slug, circuit_slug, layout_slug)
     if not layout_details:
         raise HTTPException(status_code=404, detail="Layout not found")
-    return layout_details
+    return layout_details.to_dict()
 
 @app.get("/tracks/{country_slug}/{city_slug}/{circuit_slug}/year/{year}/{image_format}")
 async def get_track_by_year(

models/circuit.py

@@ -19,6 +19,14 @@ class Circuit:
     locality: 'Locality'
     layouts: dict[str, TrackLayout]
 
+    def to_dict(self) -> dict:
+        return {
+            "slug": self.slug,
+            "name": self.name,
+            "urls": {"wikipedia": self.urls.wikipedia, "fandom": self.urls.fandom},
+            "layouts": {k: v.to_dict() for k, v in self.layouts.items()},
+        }
+
     @classmethod
     def from_dict(cls, locality: 'Locality', slug: str, data: dict) -> 'Circuit':
         circuit = cls(

models/country.py

@@ -7,6 +7,13 @@ class Country:
     name: str
     localities: dict[str, Locality]
 
+    def to_dict(self) -> dict:
+        return {
+            "slug": self.slug,
+            "name": self.name,
+            "localities": {k: v.to_dict() for k, v in self.localities.items()},
+        }
+
     @classmethod
     def from_dict(cls, slug: str, data: dict):
         country = cls(

models/locality.py

@@ -12,6 +12,13 @@ class Locality:
     country: 'Country'
     circuits: dict[str, Circuit]
 
+    def to_dict(self) -> dict:
+        return {
+            "slug": self.slug,
+            "name": self.name,
+            "circuits": {k: v.to_dict() for k, v in self.circuits.items()},
+        }
+
     @classmethod
     def from_dict(cls, country: 'Country', slug: str, data: dict):
         locality = cls(

models/track_layout.py

@@ -27,6 +27,13 @@ class TrackLayout:
             circuit=circuit
         )
 
+    def to_dict(self) -> dict:
+        return {
+            "slug": self.slug,
+            "description": self.description,
+            "imageUrl": self.imageUrl,
+        }
+
     @property
     def coordinates(self) -> list[tuple[float, float]]:
         return self._geo_data.features[0].geometry.coordinates