feat: 공정 관리 API 개선 및 ProcessItem 추가

- ProcessItem 모델 및 마이그레이션 추가
- Process 요청/서비스 로직 수정
- Swagger API 문서 추가

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

app/Models/Process.php

@@ -6,6 +6,7 @@
 use App\Traits\ModelTrait;
 use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsToMany;
 use Illuminate\Database\Eloquent\Relations\HasMany;
 use Illuminate\Database\Eloquent\SoftDeletes;
 
@@ -41,10 +42,29 @@ class Process extends Model
     ];
 
     /**
-     * 공정 자동 분류 규칙
+     * 공정 자동 분류 규칙 (패턴 규칙)
      */
     public function classificationRules(): HasMany
     {
         return $this->hasMany(ProcessClassificationRule::class)->orderBy('priority');
     }
+
+    /**
+     * 공정-품목 연결 (중간 테이블)
+     */
+    public function processItems(): HasMany
+    {
+        return $this->hasMany(ProcessItem::class)->orderBy('priority');
+    }
+
+    /**
+     * 연결된 품목 (다대다)
+     */
+    public function items(): BelongsToMany
+    {
+        return $this->belongsToMany(Items\Item::class, 'process_items')
+            ->withPivot(['priority', 'is_active'])
+            ->withTimestamps()
+            ->orderByPivot('priority');
+    }
 }

app/Models/ProcessItem.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace App\Models;
+
+use App\Models\Items\Item;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+/**
+ * 공정-품목 연결 모델 (개별 품목 지정용)
+ */
+class ProcessItem extends Model
+{
+    use HasFactory;
+
+    protected $fillable = [
+        'process_id',
+        'item_id',
+        'priority',
+        'is_active',
+    ];
+
+    protected $casts = [
+        'is_active' => 'boolean',
+        'priority' => 'integer',
+    ];
+
+    /**
+     * 공정
+     */
+    public function process(): BelongsTo
+    {
+        return $this->belongsTo(Process::class);
+    }
+
+    /**
+     * 품목
+     */
+    public function item(): BelongsTo
+    {
+        return $this->belongsTo(Item::class);
+    }
+}