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/Http/Requests/V1/Stock/StoreStockAdjustmentRequest.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Http\Requests\V1\Stock;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class StoreStockAdjustmentRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'quantity' => ['required', 'numeric', 'not_in:0'],
+            'remark' => ['nullable', 'string', 'max:500'],
+        ];
+    }
+
+    public function messages(): array
+    {
+        return [
+            'quantity.required' => __('error.stock.adjustment_qty_required'),
+            'quantity.not_in' => __('error.stock.adjustment_qty_zero'),
+        ];
+    }
+}