refactor: Remove /upload prefix from upload router for better URL structure

app/routers/upload.py

@@ -10,13 +10,13 @@ import pandas as pd
 
 from app.core.database import get_db
 
+
 router = APIRouter(
-    prefix="/upload",
     tags=["Upload"]
 )
 
 
-@router.post("/history")
+@router.post("/upload/history")
 async def upload_history(
     file: UploadFile = File(..., description="엑셀 파일 (.xlsx, .xls)"),
     plant_id: str = Form(..., description="발전소 ID (예: nrems-01)"),