fix: 统一 Excel 工作簿共享存储，修复多组件互相覆盖

office.ts（内存句柄表）、office-file-extended.ts（每次重读磁盘）、
excel-common.ts（按路径独立缓存）、extended.ts（loadSheet 每次重建）
各自持有工作簿实例并整簿写回同一文件，后保存者会整体覆盖先保存者：
列宽/行高/合并被背景色冲掉、复制的 Sheet 被新建 Sheet 冲掉等。

- 新增 excel-store.ts：按路径共享同一 ExcelJS 实例，四个模块统一接入
- resolveWorkbook 返回流程变量持有的原始句柄对象，另存为改写 path
  能同步到后续节点（此前改在副本上，下游仍写旧路径）
- 另存为后以新路径重新登记实例并释放旧路径缓存
- ReadColumn 裁掉尾部空值（共享实例下触碰空行会撑大 rowCount）
- 新增 3 个共享存储回归测试（格式保持/复制Sheet保持/另存后续写）

src/main/capabilities/excel-common.ts

@@ -2,11 +2,11 @@ import ExcelJS from "exceljs";
 import path from "node:path";
 import { register } from "../engine/registry";
 import { RuntimeError, type CapabilityHandler } from "../engine/types";
+import { acquireWorkbook, releaseWorkbook } from "./excel-store";
 
 type WorkbookSource = { workbook: ExcelJS.Workbook; filePath: string };
 type CopiedRange = { values: unknown[][]; styles: Partial<ExcelJS.Style>[][] };
 
-const workbookCache = new Map<string, ExcelJS.Workbook>();
 let copiedRange: CopiedRange | undefined;
 
 function value(args: Record<string, unknown>, keys: string[], fallback: unknown = ""): unknown {
@@ -46,12 +46,7 @@ function requiredPath(candidate: unknown, nodeId: string, componentId: string):
 
 async function loadWorkbook(args: Record<string, unknown>, nodeId: string, componentId: string): Promise<WorkbookSource> {
   const filePath = requiredPath(value(args, ["workbook", "objExcel", "objExcelWorkBook", "file", "path"]), nodeId, componentId);
-  let workbook = workbookCache.get(filePath);
-  if (!workbook) {
-    workbook = new ExcelJS.Workbook();
-    await workbook.xlsx.readFile(filePath);
-    workbookCache.set(filePath, workbook);
-  }
+  const workbook = await acquireWorkbook(filePath);
   return { workbook, filePath };
 }
 
@@ -558,7 +553,7 @@ const splitColumn: CapabilityHandler = async (_ctx, node, args) => {
 const closeWorkbook: CapabilityHandler = async (_ctx, node, args) => {
   const source = await loadWorkbook(args, node.id, node.componentId);
   if (truthy(value(args, ["save", "isSave"]), true)) await source.workbook.xlsx.writeFile(source.filePath);
-  workbookCache.delete(source.filePath);
+  releaseWorkbook(source.filePath);
   return source.filePath;
 };