fix: add sanitizeExtraBaseRPM to BatchCreate handler

Ensures base_rpm validation (clamp 0-10000) is consistent across
all four account mutation paths: Create, Update, BulkUpdate, BatchCreate.

backend/internal/handler/admin/account_handler.go

@@ -938,6 +938,9 @@ func (h *AccountHandler) BatchCreate(c *gin.Context) {
 				continue
 			}
 
+			// base_rpm 输入校验：负值归零，超过 10000 截断
+			sanitizeExtraBaseRPM(item.Extra)
+
 			skipCheck := item.ConfirmMixedChannelRisk != nil && *item.ConfirmMixedChannelRisk
 
 			account, err := h.adminService.CreateAccount(ctx, &service.CreateAccountInput{