feat(web-admin): add ListExportDropdown and Excel blob download helper

Support filtered-result primary action and optional export-selected menu.

Co-authored-by: Cursor <cursoragent@cursor.com>

web-admin/src/utils/list-export-download.ts

@@ -0,0 +1,41 @@
+/** 从 Content-Disposition 解析文件名；失败则用 fallback */
+export function filenameFromContentDisposition(
+  header: string | undefined,
+  fallback: string
+): string {
+  if (!header) return fallback
+  const utf8 = /filename\*\s*=\s*UTF-8''([^;]+)/i.exec(header)
+  if (utf8?.[1]) {
+    try {
+      return decodeURIComponent(utf8[1].trim().replace(/["']/g, ''))
+    } catch {
+      /* ignore */
+    }
+  }
+  const plain = /filename\s*=\s*("?)([^";]+)\1/i.exec(header)
+  if (plain?.[2]) return plain[2].trim()
+  return fallback
+}
+
+export function triggerBlobDownload(blob: Blob, filename: string): void {
+  const url = URL.createObjectURL(blob)
+  const link = document.createElement('a')
+  link.href = url
+  link.download = filename
+  link.click()
+  URL.revokeObjectURL(url)
+}
+
+/** Axios 成功时若拦截器已把 data 设为 Blob，直接用；否则兼容 { data: Blob, headers } */
+export function pickBlobFromExportResponse(res: any): { blob: Blob; filenameHeader?: string } {
+  if (res instanceof Blob) {
+    return { blob: res }
+  }
+  if (res?.data instanceof Blob) {
+    return {
+      blob: res.data,
+      filenameHeader: res.headers?.['content-disposition'] || res.headers?.['Content-Disposition']
+    }
+  }
+  throw new Error('导出响应不是文件')
+}