feat: 문서 관리 시스템 모델 생성 (Phase 1.2)

- Document 모델 (상태 관리, 다형성 연결, 결재 처리)
- DocumentApproval 모델 (결재 단계, 상태 처리)
- DocumentData 모델 (EAV 패턴 데이터 저장)
- DocumentAttachment 모델 (파일 첨부 연결)

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

app/Models/Documents/DocumentAttachment.php

@@ -0,0 +1,144 @@
+<?php
+
+namespace App\Models\Documents;
+
+use App\Models\Commons\File;
+use App\Models\Members\User;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+/**
+ * 문서 첨부파일 모델
+ *
+ * @property int $id
+ * @property int $document_id
+ * @property int $file_id
+ * @property string $attachment_type 첨부 유형 (general, signature, image 등)
+ * @property string|null $description 설명
+ * @property int|null $created_by
+ * @property \Carbon\Carbon|null $created_at
+ * @property \Carbon\Carbon|null $updated_at
+ */
+class DocumentAttachment extends Model
+{
+    protected $table = 'document_attachments';
+
+    // =========================================================================
+    // 첨부 유형 상수
+    // =========================================================================
+
+    public const TYPE_GENERAL = 'general';
+
+    public const TYPE_SIGNATURE = 'signature';
+
+    public const TYPE_IMAGE = 'image';
+
+    public const TYPE_REFERENCE = 'reference';
+
+    public const TYPES = [
+        self::TYPE_GENERAL,
+        self::TYPE_SIGNATURE,
+        self::TYPE_IMAGE,
+        self::TYPE_REFERENCE,
+    ];
+
+    // =========================================================================
+    // Fillable & Casts
+    // =========================================================================
+
+    protected $fillable = [
+        'document_id',
+        'file_id',
+        'attachment_type',
+        'description',
+        'created_by',
+    ];
+
+    protected $attributes = [
+        'attachment_type' => self::TYPE_GENERAL,
+    ];
+
+    // =========================================================================
+    // Relationships
+    // =========================================================================
+
+    /**
+     * 문서
+     */
+    public function document(): BelongsTo
+    {
+        return $this->belongsTo(Document::class);
+    }
+
+    /**
+     * 파일
+     */
+    public function file(): BelongsTo
+    {
+        return $this->belongsTo(File::class);
+    }
+
+    /**
+     * 생성자
+     */
+    public function creator(): BelongsTo
+    {
+        return $this->belongsTo(User::class, 'created_by');
+    }
+
+    // =========================================================================
+    // Scopes
+    // =========================================================================
+
+    /**
+     * 특정 유형의 첨부파일
+     */
+    public function scopeOfType($query, string $type)
+    {
+        return $query->where('attachment_type', $type);
+    }
+
+    /**
+     * 일반 첨부파일
+     */
+    public function scopeGeneral($query)
+    {
+        return $query->where('attachment_type', self::TYPE_GENERAL);
+    }
+
+    /**
+     * 서명 첨부파일
+     */
+    public function scopeSignatures($query)
+    {
+        return $query->where('attachment_type', self::TYPE_SIGNATURE);
+    }
+
+    /**
+     * 이미지 첨부파일
+     */
+    public function scopeImages($query)
+    {
+        return $query->where('attachment_type', self::TYPE_IMAGE);
+    }
+
+    // =========================================================================
+    // Helper Methods
+    // =========================================================================
+
+    /**
+     * 서명 첨부파일 여부
+     */
+    public function isSignature(): bool
+    {
+        return $this->attachment_type === self::TYPE_SIGNATURE;
+    }
+
+    /**
+     * 이미지 첨부파일 여부
+     */
+    public function isImage(): bool
+    {
+        return $this->attachment_type === self::TYPE_IMAGE;
+    }
+}