feat: back button + reopen for approved/rejected tickets

backend/src/main/java/com/srsystem/controller/TicketController.java

@@ -135,6 +135,13 @@ public class TicketController {
         return ResponseEntity.ok(ApiResponse.ok("반려되었습니다", ticketService.rejectTicket(ticketId, currentUser.getEmpId(), body.get("reason"))));
     }
 
+    @Operation(summary = "티켓 재오픈", description = "APPROVED/REJECTED 상태를 PENDING_APPROVAL로 되돌립니다")
+    @PreAuthorize("hasAnyRole('MANAGER', 'ADMIN')")
+    @PostMapping("/{ticketId}/reopen")
+    public ResponseEntity<ApiResponse<IssueTicket>> reopenTicket(@PathVariable Long ticketId) {
+        return ResponseEntity.ok(ApiResponse.ok("재오픈되었습니다", ticketService.reopenTicket(ticketId)));
+    }
+
     @Operation(summary = "댓글 목록 조회", description = "티켓의 댓글 목록을 조회합니다")
     @PreAuthorize("hasAnyRole('EMPLOYEE', 'MANAGER', 'ADMIN')")
     @GetMapping("/{ticketId}/comments")

backend/src/main/java/com/srsystem/service/TicketService.java

@@ -234,6 +234,19 @@ public class TicketService {
         return toIssueTicket(ticketRepository.save(ticket));
     }
 
+    @Transactional
+    public IssueTicket reopenTicket(Long ticketId) {
+        Ticket ticket = ticketRepository.findById(ticketId)
+                .orElseThrow(() -> new BusinessException(ErrorCode.TICKET_NOT_FOUND));
+        if (ticket.getStatus() != TicketStatus.APPROVED && ticket.getStatus() != TicketStatus.REJECTED) {
+            throw new BusinessException(ErrorCode.INVALID_STATUS);
+        }
+        ticket.setStatus(TicketStatus.PENDING_APPROVAL);
+        ticket.setApprovedBy(null);
+        ticket.setApprovedAt(null);
+        return toIssueTicket(ticketRepository.save(ticket));
+    }
+
     private IssueTicket toIssueTicket(Ticket ticket) {
         return new IssueTicket(
                 ticket.getTicketId(),

src/app/(main)/issues/[id]/page.tsx

@@ -1,7 +1,7 @@
 'use client';
 
 import React, { useState, useEffect } from 'react';
-import { ChevronLeft, Clock, User, MessageSquare, Paperclip, Send, CheckCircle2, ArrowRight } from 'lucide-react';
+import { ChevronLeft, Clock, User, MessageSquare, Paperclip, Send, CheckCircle2, ArrowRight, RotateCcw } from 'lucide-react';
 import Link from 'next/link';
 import ticketService from '@/services/ticketService';
 import apiClient from '@/services/apiClient';
@@ -72,7 +72,10 @@ export default function IssueDetailPage({ params }: { params: Promise<{ id: stri
 
   const currentIdx = statusFlow.indexOf(status);
   const canAdvance = currentIdx < statusFlow.length - 1;
+  const canGoBack = currentIdx > 0;
   const isClosed = status === 'CLOSED';
+  const isApprovalTicket = ['VACATION', 'EXPENSE', 'EQUIPMENT_REQUEST', 'GENERAL'].includes(ticket?.category || '');
+  const isMgmt = user?.roleCode !== 'EMPLOYEE';
 
   const handleAdvance = async () => {
     if (!canAdvance) return;
@@ -85,6 +88,24 @@ export default function IssueDetailPage({ params }: { params: Promise<{ id: stri
     }
   };
 
+  const handleBack = async () => {
+    if (!canGoBack) return;
+    const prevStatus = statusFlow[currentIdx - 1];
+    try {
+      await ticketService.updateStatus(ticketId, prevStatus);
+      setStatus(prevStatus);
+    } catch (err: unknown) {
+      alert((err as { message?: string })?.message || '상태 변경 실패');
+    }
+  };
+
+  const handleReopen = async () => {
+    try {
+      const res: any = await apiClient.post(`/tickets/${ticketId}/reopen`);
+      if (res.success) setTicket(res.data);
+    } catch (err: any) { alert(err.message || '재오픈 실패'); }
+  };
+
   const handlePostComment = async () => {
     if (!newComment.trim()) return;
     try {
@@ -124,10 +145,27 @@ export default function IssueDetailPage({ params }: { params: Promise<{ id: stri
           </Link>
           <div className="flex flex-wrap items-center gap-3">
             <span className={`text-xs font-semibold px-3 py-1.5 rounded-full ${statusColor[status]}`}>{statusLabel[status]}</span>
-            {!isClosed && (
+            {!isClosed && statusFlow.includes(status) && (
+              <>
+                {canGoBack && (
+                  <button onClick={handleBack} className="bg-gray-100 hover:bg-gray-200 text-text-muted text-xs font-semibold px-3 py-1.5 rounded-lg transition-all flex items-center">
+                    <ChevronLeft className="w-3.5 h-3.5 mr-1" /> Back
+                  </button>
+                )}
                 <button onClick={handleAdvance} disabled={!canAdvance} className="bg-primary hover:bg-primary-hover disabled:opacity-40 disabled:cursor-not-allowed text-white text-xs font-semibold px-4 py-1.5 rounded-lg transition-all flex items-center">
                   {canAdvance ? <>Advance <ArrowRight className="w-3.5 h-3.5 ml-1.5" /></> : 'Completed'}
                 </button>
+              </>
+            )}
+            {status === 'APPROVED' && isMgmt && (
+              <button onClick={handleReopen} className="bg-amber-50 hover:bg-amber-100 text-amber-700 border border-amber-200 text-xs font-semibold px-3 py-1.5 rounded-lg transition-all">
+                승인 취소
+              </button>
+            )}
+            {status === 'REJECTED' && (
+              <button onClick={handleReopen} className="bg-blue-50 hover:bg-blue-100 text-blue-700 border border-blue-200 text-xs font-semibold px-3 py-1.5 rounded-lg transition-all">
+                재오픈
+              </button>
             )}
           </div>
         </div>