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/Sales/Services/SalesService.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace App\Modules\Sales\Services;
+
+use App\Modules\Sales\Contracts\SalesServiceInterface;
+use App\Modules\Sales\Models\SalesImportItem;
+use Illuminate\Support\Facades\DB;
+
+class SalesService implements SalesServiceInterface
+{
+    public function getThisMonthRevenue(): float
+    {
+        return (float) SalesImportItem::whereMonth('transaction_at', now()->month)
+            ->whereYear('transaction_at', now()->year)
+            ->sum('amount');
+    }
+
+    public function getSalesTrend(int $days = 30): array
+    {
+        $startDate = now()->subDays($days - 1)->startOfDay();
+        $salesData = SalesImportItem::where('transaction_at', '>=', $startDate)
+            ->selectRaw('DATE(transaction_at) as date, SUM(amount) as total')
+            ->groupBy('date')
+            ->orderBy('date')
+            ->get()
+            ->mapWithKeys(function ($item) {
+                return [$item->date => (int)$item->total];
+            });
+
+        $salesTrend = [];
+        for ($i = 0; $i < $days; $i++) {
+            $date = $startDate->copy()->addDays($i)->format('Y-m-d');
+            $salesTrend[] = [
+                'date' => $startDate->copy()->addDays($i)->format('m/d'),
+                'amount' => $salesData[$date] ?? 0,
+            ];
+        }
+        
+        return $salesTrend;
+    }
+
+    public function getTopSellingProducts(int $limit = 5): \Illuminate\Support\Collection
+    {
+        return SalesImportItem::whereMonth('transaction_at', now()->month)
+            ->whereYear('transaction_at', now()->year)
+            ->select('product_code', 'product_id', DB::raw('SUM(amount) as total_amount'))
+            ->groupBy('product_code', 'product_id')
+            ->orderByDesc('total_amount')
+            ->limit($limit)
+            ->get();
+    }
+
+    public function getTopSellingByQuantity(int $limit = 5): \Illuminate\Support\Collection
+    {
+        return SalesImportItem::whereMonth('transaction_at', now()->month)
+            ->whereYear('transaction_at', now()->year)
+            ->select('product_code', 'product_id', DB::raw('SUM(quantity) as total_quantity'))
+            ->groupBy('product_code', 'product_id')
+            ->orderByDesc('total_quantity')
+            ->limit($limit)
+            ->get();
+    }
+}