feat: Item Master 하이브리드 구조 전환 및 독립 API 추가

- CASCADE FK → 독립 엔티티 + entity_relationships 링크 테이블
- 독립 API 10개 추가 (섹션/필드/BOM CRUD, clone, usage)
- SectionTemplate 모델 제거 → ItemSection.is_template 통합
- 페이지-섹션, 섹션-필드, 섹션-BOM 링크/언링크 API 14개 추가
- Swagger 문서 업데이트

app/Http/Requests/ItemMaster/IndependentBomItemStoreRequest.php

@@ -0,0 +1,28 @@
+<?php
+
+namespace App\Http\Requests\ItemMaster;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class IndependentBomItemStoreRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'group_id' => 'nullable|integer',
+            'item_code' => 'nullable|string|max:100',
+            'item_name' => 'required|string|max:255',
+            'quantity' => 'nullable|numeric|min:0',
+            'unit' => 'nullable|string|max:50',
+            'unit_price' => 'nullable|numeric|min:0',
+            'total_price' => 'nullable|numeric|min:0',
+            'spec' => 'nullable|string',
+            'note' => 'nullable|string',
+        ];
+    }
+}

app/Http/Requests/ItemMaster/IndependentFieldStoreRequest.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Http\Requests\ItemMaster;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class IndependentFieldStoreRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'group_id' => 'nullable|integer',
+            'field_name' => 'required|string|max:255',
+            'field_type' => 'required|in:textbox,number,dropdown,checkbox,date,textarea',
+            'is_required' => 'nullable|boolean',
+            'default_value' => 'nullable|string',
+            'placeholder' => 'nullable|string|max:255',
+            'display_condition' => 'nullable|array',
+            'validation_rules' => 'nullable|array',
+            'options' => 'nullable|array',
+            'properties' => 'nullable|array',
+        ];
+    }
+}

app/Http/Requests/ItemMaster/IndependentSectionStoreRequest.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace App\Http\Requests\ItemMaster;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class IndependentSectionStoreRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'group_id' => 'nullable|integer',
+            'title' => 'required|string|max:255',
+            'type' => 'required|in:fields,bom',
+            'is_template' => 'nullable|boolean',
+            'is_default' => 'nullable|boolean',
+            'description' => 'nullable|string',
+        ];
+    }
+}

app/Http/Requests/ItemMaster/LinkEntityRequest.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace App\Http\Requests\ItemMaster;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class LinkEntityRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'child_id' => 'required|integer|min:1',
+            'order_no' => 'nullable|integer|min:0',
+        ];
+    }
+
+    public function messages(): array
+    {
+        return [
+            'child_id.required' => __('validation.required', ['attribute' => '연결 대상 ID']),
+            'child_id.integer' => __('validation.integer', ['attribute' => '연결 대상 ID']),
+            'child_id.min' => __('validation.min.numeric', ['attribute' => '연결 대상 ID', 'min' => 1]),
+        ];
+    }
+}

app/Http/Requests/ItemMaster/ReorderRelationshipsRequest.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace App\Http\Requests\ItemMaster;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class ReorderRelationshipsRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'parent_type' => 'required|string|in:page,section',
+            'parent_id' => 'required|integer|min:1',
+            'ordered_items' => 'required|array|min:1',
+            'ordered_items.*.child_type' => 'required|string|in:section,field,bom',
+            'ordered_items.*.child_id' => 'required|integer|min:1',
+        ];
+    }
+
+    public function messages(): array
+    {
+        return [
+            'parent_type.required' => __('validation.required', ['attribute' => '부모 타입']),
+            'parent_type.in' => __('validation.in', ['attribute' => '부모 타입']),
+            'parent_id.required' => __('validation.required', ['attribute' => '부모 ID']),
+            'ordered_items.required' => __('validation.required', ['attribute' => '정렬 항목']),
+            'ordered_items.array' => __('validation.array', ['attribute' => '정렬 항목']),
+        ];
+    }
+}