feat(api): item_master_fields 속성을 item_fields로 이관

- item_fields에 category, description, is_common 컬럼 추가
- section_id를 nullable로 변경 (독립 필드 지원)
- item_master_fields 데이터를 item_fields로 이관 (section_id = NULL)
- 기존 item_master_fields 테이블 유지 (하위 호환성)

database/migrations/2025_11_26_230132_add_master_field_columns_to_item_fields_table.php

@@ -0,0 +1,102 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+/**
+ * item_master_fields 테이블 통합
+ *
+ * 목적: item_master_fields의 속성을 item_fields에 추가하고 데이터 이관
+ *
+ * 변경 내용:
+ * 1. item_fields의 section_id를 nullable로 변경 (독립 필드 지원)
+ * 2. item_fields에 category, description, is_common 컬럼 추가
+ * 3. item_master_fields 데이터를 item_fields로 이관
+ * 4. item_master_fields 테이블은 유지 (하위 호환성, 추후 삭제)
+ *
+ * 참고: FK (fk_item_fields_section)는 2025_11_26_100001에서 이미 제거됨
+ */
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        // 1. section_id를 nullable로 변경 (이미 nullable이면 스킵)
+        $sectionIdColumn = DB::selectOne("SHOW COLUMNS FROM item_fields WHERE Field = 'section_id'");
+        if ($sectionIdColumn && $sectionIdColumn->Null === 'NO') {
+            Schema::table('item_fields', function (Blueprint $table) {
+                $table->unsignedBigInteger('section_id')->nullable()->comment('섹션 ID (NULL = 독립 필드)')->change();
+            });
+        }
+
+        // 2. item_fields에 컬럼 추가 (이미 있으면 스킵)
+        if (! Schema::hasColumn('item_fields', 'category')) {
+            Schema::table('item_fields', function (Blueprint $table) {
+                $table->string('category', 100)->nullable()->after('properties')->comment('카테고리');
+                $table->text('description')->nullable()->after('category')->comment('설명');
+                $table->boolean('is_common')->default(false)->after('description')->comment('공통 필드 여부');
+            });
+        }
+
+        // 3. item_master_fields 데이터를 item_fields로 이관
+        DB::statement('
+            INSERT INTO item_fields (
+                tenant_id, group_id, section_id, field_name, field_type,
+                order_no, is_required, default_value, placeholder,
+                display_condition, validation_rules, options, properties,
+                category, description, is_common,
+                created_by, updated_by, deleted_by,
+                created_at, updated_at, deleted_at
+            )
+            SELECT
+                m.tenant_id,
+                COALESCE(m.group_id, 1) as group_id,
+                NULL as section_id,
+                m.field_name,
+                m.field_type,
+                0 as order_no,
+                0 as is_required,
+                m.default_value,
+                NULL as placeholder,
+                NULL as display_condition,
+                m.validation_rules,
+                m.options,
+                m.properties,
+                m.category,
+                m.description,
+                m.is_common,
+                m.created_by,
+                m.updated_by,
+                m.deleted_by,
+                m.created_at,
+                m.updated_at,
+                m.deleted_at
+            FROM item_master_fields m
+        ');
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        // 이관된 데이터 삭제 (section_id = null인 레코드)
+        DB::table('item_fields')
+            ->whereNull('section_id')
+            ->delete();
+
+        // 컬럼 삭제
+        Schema::table('item_fields', function (Blueprint $table) {
+            $table->dropColumn(['category', 'description', 'is_common']);
+        });
+
+        // section_id를 NOT NULL로 복원
+        Schema::table('item_fields', function (Blueprint $table) {
+            $table->unsignedBigInteger('section_id')->nullable(false)->comment('섹션 ID')->change();
+        });
+    }
+};