feat: 기존 작업에 이슈 추가 Import 기능

- ImportService에 importIssuesToTask 메서드 추가
- ImportController에 importIssues 액션 추가
- ImportIssuesRequest FormRequest 생성
- POST /api/admin/pm/import/task/{taskId}/issues 라우트 추가
- import.blade.php UI에 '기존 작업에 이슈 추가' 모드 추가
- ImportProjectRequest에 tasks 레벨 검증 규칙 보완

app/Http/Requests/ProjectManagement/ImportIssuesRequest.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace App\Http\Requests\ProjectManagement;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class ImportIssuesRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'issues' => 'required|array|min:1',
+            'issues.*.title' => 'required|string|max:255',
+            'issues.*.description' => 'nullable|string',
+            'issues.*.type' => 'nullable|in:bug,feature,improvement',
+            'issues.*.status' => 'nullable|in:open,in_progress,resolved,closed',
+            // 일정 관련
+            'issues.*.start_date' => 'nullable|date',
+            'issues.*.due_date' => 'nullable|date|after_or_equal:issues.*.start_date',
+            'issues.*.estimated_hours' => 'nullable|integer|min:0',
+            'issues.*.is_urgent' => 'nullable|boolean',
+            // 팀/담당자/고객사 (하이브리드)
+            'issues.*.department_id' => 'nullable|integer|exists:departments,id',
+            'issues.*.team' => 'nullable|string|max:100',
+            'issues.*.assignee_id' => 'nullable|integer|exists:users,id',
+            'issues.*.assignee_name' => 'nullable|string|max:100',
+            'issues.*.client' => 'nullable|string|max:100',
+        ];
+    }
+
+    public function messages(): array
+    {
+        return [
+            'issues.required' => 'issues 배열은 필수입니다.',
+            'issues.min' => '최소 1개 이상의 이슈가 필요합니다.',
+            'issues.*.title.required' => '각 이슈의 title은 필수입니다.',
+        ];
+    }
+}