refactor: 重構模組通訊與調整儀表板功能

- 依循跨模組通訊規範，將 Sales 與 Production 模組中對 Inventory 的直接模型關聯改為透過 InventoryServiceInterface 取得
- 於 InventoryService 實作獲取最高庫存價值、即將過期商品等方法，供儀表板使用
- 確保所有跨模組調用皆採用手動水和（Manual Hydration）方式組合資料
- 移除本地已歸檔的 .agent 規範檔案

app/Modules/Production/Contracts/ProductionServiceInterface.php

@@ -0,0 +1,8 @@
+<?php
+
+namespace App\Modules\Production\Contracts;
+
+interface ProductionServiceInterface
+{
+    public function getPendingProductionCount(): int;
+}

app/Modules/Production/Models/RecipeItem.php

@@ -27,13 +27,5 @@ class RecipeItem extends Model
         return $this->belongsTo(Recipe::class);
     }
 
-    public function product()
-    {
-        return $this->belongsTo(\App\Modules\Inventory\Models\Product::class);
-    }
-
-    public function unit()
-    {
-        return $this->belongsTo(\App\Modules\Inventory\Models\Unit::class);
-    }
+    // product 和 unit 關聯移至 service (跨模組)
 }

app/Modules/Production/ProductionServiceProvider.php

@@ -10,7 +10,10 @@ class ProductionServiceProvider extends ServiceProvider
 {
     public function register(): void
     {
-        //
+        $this->app->bind(
+            \App\Modules\Production\Contracts\ProductionServiceInterface::class,
+            \App\Modules\Production\Services\ProductionService::class
+        );
     }
 
     public function boot(): void

app/Modules/Production/Services/ProductionService.php

@@ -0,0 +1,14 @@
+<?php
+
+namespace App\Modules\Production\Services;
+
+use App\Modules\Production\Contracts\ProductionServiceInterface;
+use App\Modules\Production\Models\ProductionOrder;
+
+class ProductionService implements ProductionServiceInterface
+{
+    public function getPendingProductionCount(): int
+    {
+        return ProductionOrder::where('status', 'pending')->count();
+    }
+}