fix: add missing _public_base_url helper

-agent_card endpoint requires base URL extraction from request
-adds utility function to construct correct base URL from Request object

main.py

@@ -46,6 +46,14 @@ def _ensure_agent() -> CloudCoderAgent:
     return _agent
 
 
+def _public_base_url(request: Request) -> str:
+    """Extract the public base URL from the request."""
+    base_url = str(request.base_url)
+    if base_url.endswith("/"):
+        base_url = base_url[:-1]
+    return base_url
+
+
 # A2A JSON-RPC 2.0 endpoint
 async def handle_a2a_message(request: Request) -> JSONResponse:
     """Handle A2A JSON-RPC 2.0 message/send requests."""
@@ -253,6 +261,7 @@ async def health() -> JSONResponse:
         }
     )
 
+
 # Agent card endpoint
 @app.get("/.well-known/agent-card.json")
 async def agent_card(request: Request) -> JSONResponse:
@@ -287,5 +296,6 @@ app.mount("/", gradio_app.app)
 
 if __name__ == "__main__":
     import uvicorn
+
     print("🚀 Starting uvicorn on port", int(os.getenv("PORT", 7860)))
     uvicorn.run(app, host="0.0.0.0", port=int(os.getenv("PORT", 7860)))