feat: add one-to-one box mode with duplicate bind check

Add box_mode field to BoxSaveRequest and DuplicateZongpaiBindError
exception. In one-to-one mode, prevent the same zongpai from being
packed into multiple boxes, returning 409 with existing box info.

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

app/main.py

@@ -19,7 +19,7 @@ except Exception as e:
 from app.api.v1.location import router as location_router
 from app.api.v1.box import router as box_router
 from app.services.location_service import DuplicateLocationError
-from app.services.box_service import ZongpaiNotFoundError, DuplicateBoxItemError, InvalidZongpaiError
+from app.services.box_service import ZongpaiNotFoundError, DuplicateBoxItemError, InvalidZongpaiError, DuplicateZongpaiBindError
 
 app = FastAPI(title="CargoTrace API", version="0.1.0")
 
@@ -106,6 +106,20 @@ async def duplicate_box_handler(request: Request, exc: DuplicateBoxItemError):
     )
 
 
+@app.exception_handler(DuplicateZongpaiBindError)
+async def duplicate_zongpai_bind_handler(request: Request, exc: DuplicateZongpaiBindError):
+    return JSONResponse(
+        status_code=409,
+        content={
+            "error_code": "DUPLICATE_ZONGPAI_BIND",
+            "message": f"总排号 {exc.zongpai_no} 已绑定箱号 {exc.box_no}，请勿重复装箱",
+            "paichan_no": exc.paichan_no,
+            "box_no": exc.box_no,
+            "zongpai_no": exc.zongpai_no,
+        },
+    )
+
+
 @app.get("/")
 async def root():
     return {"message": "Welcome to CargoTrace API"}