feat: [pm] 이슈 일정 필드 추가 마이그레이션

- admin_pm_issues 테이블에 start_date, due_date, estimated_hours 컬럼 추가
- due_date 인덱스 추가

database/migrations/2025_12_02_155241_add_schedule_fields_to_admin_pm_issues_table.php

@@ -0,0 +1,36 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * admin_pm_issues 테이블에 일정 관련 필드 추가
+     */
+    public function up(): void
+    {
+        Schema::table('admin_pm_issues', function (Blueprint $table) {
+            $table->date('start_date')->nullable()->after('status')->comment('시작일');
+            $table->date('due_date')->nullable()->after('start_date')->comment('마감일');
+            $table->unsignedInteger('estimated_hours')->nullable()->after('due_date')->comment('예상 시간(시)');
+
+            // 인덱스
+            $table->index('due_date', 'idx_admin_pm_issues_due_date');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('admin_pm_issues', function (Blueprint $table) {
+            $table->dropIndex('idx_admin_pm_issues_due_date');
+            $table->dropColumn(['start_date', 'due_date', 'estimated_hours']);
+        });
+    }
+};