feat: [stock] 재고 조정 API 추가

- GET /stocks/{id}/adjustments: 조정 이력 조회
- POST /stocks/{id}/adjustments: 조정 등록 (증감 수량 + 사유)
- StockTransaction에 adjustment reason 추가
- StoreStockAdjustmentRequest 검증 추가

app/Models/Tenants/StockTransaction.php

@@ -50,6 +50,8 @@ class StockTransaction extends Model
 
     public const REASON_PRODUCTION_OUTPUT = 'production_output';
 
+    public const REASON_ADJUSTMENT = 'adjustment';
+
     public const REASONS = [
         self::REASON_RECEIVING => '입고',
         self::REASON_WORK_ORDER_INPUT => '생산투입',
@@ -57,6 +59,7 @@ class StockTransaction extends Model
         self::REASON_ORDER_CONFIRM => '수주확정',
         self::REASON_ORDER_CANCEL => '수주취소',
         self::REASON_PRODUCTION_OUTPUT => '생산입고',
+        self::REASON_ADJUSTMENT => '재고조정',
     ];
 
     protected $fillable = [