fix: correct Excel header for product unit from "单位" to "产品单位"

The product unit column header was incorrectly showing "单位" instead of
"产品单位", causing confusion with the material unit column which also
uses "单位". Fixed in both extractor.ts and excel-parser.ts.

Co-Authored-By: Claude (glm-5) <noreply@anthropic.com>

src/main/services/erp/extractor.ts

@@ -340,7 +340,7 @@ export class ExtractorService {
       { header: '产品编码', key: 'productCode', width: 15 },
       { header: '产品名称', key: 'productName', width: 30 },
       { header: '产品计划数量', key: 'productPlannedQuantity', width: 15 },
-      { header: '单位', key: 'productUnit', width: 10 },
+      { header: '产品单位', key: 'productUnit', width: 10 },
       { header: '用料部门', key: 'department', width: 15 },
       { header: '备注', key: 'remark', width: 20 },
       { header: '制单人', key: 'creator', width: 15 },

src/main/services/excel/excel-parser.ts

@@ -158,7 +158,7 @@ export class ExcelParser {
       { header: '产品编码', key: 'productCode', width: 15 },
       { header: '产品名称', key: 'productName', width: 30 },
       { header: '产品计划数量', key: 'productPlannedQuantity', width: 15 },
-      { header: '单位', key: 'productUnit', width: 10 },
+      { header: '产品单位', key: 'productUnit', width: 10 },
       { header: '用料部门', key: 'department', width: 15 },
       { header: '备注', key: 'remark', width: 20 },
       { header: '制单人', key: 'creator', width: 15 },