fix: 审批流程三个bug修复

1. 点通过不再重复创建审批记录(后端无NULL记录时返回400而非自动创建)
2. 非提交人不再显示撤销按钮(列表页增加applicant_id校验)
3. 已审批工单不再显示通过/拒绝按钮(is_approver只计算pending记录)
4. 前端审批失败时弹出错误提示而非静默忽略

frontend/src/pages/TicketsPage.tsx

@@ -6,7 +6,7 @@ import {
   ArrowUpDown, Ban, ChevronLeft, AlertTriangle,
 } from 'lucide-react';
 import { statusMap, statusColorMap, dbTypeColorMap } from '@/lib/constants';
-import { useActionPermission } from '@/hooks/useAuth';
+import { useActionPermission, useAuth } from '@/hooks/useAuth';
 import PageHeader from '@/components/PageHeader';
 import EmptyState from '@/components/EmptyState';
 import { ticketApi } from '@/api/ticket';
@@ -190,6 +190,7 @@ function TableRowSkeleton() {
 /* ------------------------------------------------------------------ */
 export default function TicketsPage() {
   const navigate = useNavigate();
+  const { user: currentUser } = useAuth();
   const canCreate = useActionPermission('ticket.create');
   const canApprove = useActionPermission('ticket.approve');
   const canExecute = useActionPermission('ticket.execute');
@@ -455,7 +456,10 @@ export default function TicketsPage() {
                                 try {
                                   await ticketApi.review(ticket.id, { action: 'approve', comment: '通过' });
                                   fetchTickets(); fetchStats();
-                                } catch { /* ignore */ }
+                                } catch (e: any) {
+                                  const msg = e?.response?.data?.detail || e?.message || '审批失败';
+                                  alert(msg);
+                                }
                               }}
                               className="dg-btn dg-btn-sm dg-btn-ghost text-green-400 hover:text-green-300"
                             >
@@ -470,7 +474,10 @@ export default function TicketsPage() {
                                 try {
                                   await ticketApi.review(ticket.id, { action: 'reject', comment: '拒绝' });
                                   fetchTickets(); fetchStats();
-                                } catch { /* ignore */ }
+                                } catch (e: any) {
+                                  const msg = e?.response?.data?.detail || e?.message || '操作失败';
+                                  alert(msg);
+                                }
                               }}
                               className="dg-btn dg-btn-sm dg-btn-ghost text-red-400 hover:text-red-300"
                             >
@@ -494,7 +501,7 @@ export default function TicketsPage() {
                             </button>
                           )}
 
-                          {(ticket.status === 'pending' || ticket.status === 'reviewing' || ticket.status === 'approved') && (
+                          {currentUser?.id === ticket.applicant_id && (ticket.status === 'pending' || ticket.status === 'reviewing' || ticket.status === 'approved') && (
                             <button
                               onClick={async () => {
                                 try {