fix: unify error response format with error_code, message and domain fields

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/main.py

@@ -1,26 +1,55 @@
 from fastapi import FastAPI, Request
+from fastapi.exceptions import RequestValidationError
 from fastapi.responses import JSONResponse
 
 from app.api.v1.location import router as location_router
+from app.services.location_service import DuplicateLocationError
 
 app = FastAPI(title="CargoTrace API", version="0.1.0")
 
 app.include_router(location_router, prefix="/CargoTrace")
 
 
+@app.exception_handler(DuplicateLocationError)
+async def duplicate_location_handler(request: Request, exc: DuplicateLocationError):
+    return JSONResponse(
+        status_code=409,
+        content={
+            "error_code": "DUPLICATE_LOCATION",
+            "message": "该总排号已存在货位记录",
+            "location_code": exc.location_code,
+            "registered_at": exc.registered_at,
+        },
+    )
+
+
+@app.exception_handler(RequestValidationError)
+async def validation_error_handler(request: Request, exc: RequestValidationError):
+    for err in exc.errors():
+        msg = err.get("msg", "")
+        if "INVALID_ZONGPAI" in msg or "INVALID_LOCATION" in msg:
+            error_code = msg.replace("Value error, ", "")
+            return JSONResponse(
+                status_code=400,
+                content={
+                    "error_code": error_code,
+                    "message": error_code,
+                },
+            )
+    return JSONResponse(
+        status_code=422,
+        content={"detail": exc.errors()},
+    )
+
+
 @app.exception_handler(ValueError)
 async def value_error_handler(request: Request, exc: ValueError):
     error_code = str(exc)
-    status_map = {
-        "INVALID_ZONGPAI": 400,
-        "INVALID_LOCATION": 400,
-    }
-    status = status_map.get(error_code, 400)
     return JSONResponse(
-        status_code=status,
+        status_code=400,
         content={
             "error_code": error_code,
-            "message": str(exc),
+            "message": error_code,
         },
     )