feat(stock-count): 新增盤點差異報表彙整

前置功能分支 F1，供後續匯出功能依賴

src/modules/stock-count.ts

@@ -18,3 +18,18 @@ export interface StockCountDiff {
  * @returns 實盤減帳面的差異值
  */
 export const diffQty = (diff: StockCountDiff): number => diff.countedQty - diff.bookQty;
+
+/** 盤點差異報表列 */
+export interface StockCountReportRow {
+  /** 物料識別碼 */
+  materialId: string;
+  /** 該物料的差異量 */
+  diff: number;
+}
+
+/**
+ * 依盤點資料彙整差異報表
+ * @param diffs - 盤點差異清單
+ * @returns 逐物料的差異報表列
+ */
+export const buildReport = (diffs: StockCountDiff[]): StockCountReportRow[] => diffs.map((diff) => ({ materialId: diff.materialId, diff: diffQty(diff) }));