feat: 문서 관리 시스템 MNG 관리자 패널 구현 (Phase 2)

- Document 관련 모델 4개 생성 (Document, DocumentApproval, DocumentData, DocumentAttachment)
- DocumentController 생성 (목록/생성/상세/수정 페이지)
- DocumentApiController 생성 (AJAX CRUD 처리)
- 문서 관리 뷰 3개 생성 (index, edit, show)
- 웹/API 라우트 등록

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/Models/Documents/DocumentData.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace App\Models\Documents;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+class DocumentData extends Model
+{
+    protected $table = 'document_data';
+
+    protected $fillable = [
+        'document_id',
+        'section_id',
+        'column_id',
+        'row_index',
+        'field_key',
+        'field_value',
+    ];
+
+    protected $casts = [
+        'row_index' => 'integer',
+    ];
+
+    // =========================================================================
+    // Relationships
+    // =========================================================================
+
+    public function document(): BelongsTo
+    {
+        return $this->belongsTo(Document::class);
+    }
+
+    // =========================================================================
+    // Scopes
+    // =========================================================================
+
+    public function scopeForSection($query, int $sectionId)
+    {
+        return $query->where('section_id', $sectionId);
+    }
+
+    public function scopeForField($query, string $fieldKey)
+    {
+        return $query->where('field_key', $fieldKey);
+    }
+}