支持客户、对话记录与统计报告 CSV 导出

- 新增 /customers/export、/sessions/export、/statistics/export
- 沿用列表筛选与角色可见范围，UTF-8 BOM 便于 Excel 打开
- 前端三处导出按钮接入真实下载

web/src/pages/agent/Customers.tsx

@@ -8,7 +8,7 @@ import {
   DeleteOutlined, ExportOutlined, CloseOutlined, GlobalOutlined, MessageOutlined,
 } from '@ant-design/icons'
 import {
-  createCustomer, deleteCustomer, getCustomer, getCustomers, updateCustomer,
+  createCustomer, deleteCustomer, exportCustomersCSV, getCustomer, getCustomers, updateCustomer,
   type Customer, type Session,
 } from '@/services/api'
 import { useAuth } from '@/stores/auth'
@@ -140,6 +140,7 @@ const Customers = () => {
   const [page, setPage] = useState(1)
   const [pageSize, setPageSize] = useState(10)
   const [search, setSearch] = useState('')
+  const [exporting, setExporting] = useState(false)
   const [tagFilter, setTagFilter] = useState('all')
   const [selectedCustomer, setSelectedCustomer] = useState<Customer | null>(null)
   const [editingId, setEditingId] = useState<number | null>(null)
@@ -321,8 +322,19 @@ const Customers = () => {
               <div className="flex items-center gap-2 ml-auto">
                 <Button
                   icon={<ExportOutlined />}
+                  loading={exporting}
                   className="!text-[13px] !h-8 !px-3 !font-medium !text-neutral-600 !border-neutral-200"
-                  onClick={() => message.info('导出功能后续版本提供')}
+                  onClick={async () => {
+                    setExporting(true)
+                    try {
+                      await exportCustomersCSV({ search: search || undefined })
+                      message.success('客户列表已导出')
+                    } catch (e) {
+                      message.error(e instanceof Error ? e.message : '导出失败')
+                    } finally {
+                      setExporting(false)
+                    }
+                  }}
                 >
                   导出
                 </Button>