feat: 修正庫存與撥補單邏輯並整合文件

1. 修復倉庫統計數據加總與樣式。
2. 修正可用庫存計算邏輯（排除不可銷售倉庫）。
3. 撥補單商品列表加入批號與效期顯示。
4. 修正撥補單儲存邏輯以支援精確批號轉移。
5. 整合 FEATURES.md 至 README.md。

app/Modules/Inventory/Contracts/InventoryServiceInterface.php

@@ -0,0 +1,100 @@
+<?php
+
+namespace App\Modules\Inventory\Contracts;
+
+interface InventoryServiceInterface
+{
+    /**
+     * Check if a product has sufficient stock in a specific warehouse.
+     *
+     * @param int $productId
+     * @param int $warehouseId
+     * @param float $quantity
+     * @return bool
+     */
+    public function checkStock(int $productId, int $warehouseId, float $quantity): bool;
+
+    /**
+     * Decrease stock for a product (e.g., when an order is placed).
+     * 
+     * @param int $productId
+     * @param int $warehouseId
+     * @param float $quantity
+     * @param string|null $reason
+     * @return void
+     */
+    public function decreaseStock(int $productId, int $warehouseId, float $quantity, ?string $reason = null): void;
+
+    /**
+     * Get all active warehouses.
+     * 
+     * @return \Illuminate\Support\Collection
+     */
+    public function getAllWarehouses();
+
+    /**
+     * Get multiple products by their IDs.
+     * 
+     * @param array $ids
+     * @return \Illuminate\Support\Collection
+     */
+    public function getProductsByIds(array $ids);
+
+    /**
+     * Get a specific product by ID.
+     * 
+     * @param int $id
+     * @return object|null
+     */
+    public function getProduct(int $id);
+
+    /**
+     * Get a specific warehouse by ID.
+     * 
+     * @param int $id
+     * @return object|null
+     */
+    public function getWarehouse(int $id);
+
+    /**
+     * Get all available inventories in a specific warehouse.
+     * 
+     * @param int $warehouseId
+     * @return \Illuminate\Support\Collection
+     */
+    public function getInventoriesByWarehouse(int $warehouseId);
+
+    /**
+     * Get all products.
+     * 
+     * @return \Illuminate\Support\Collection
+     */
+    public function getAllProducts();
+
+    /**
+     * Get all units.
+     * 
+     * @return \Illuminate\Support\Collection
+     */
+    public function getUnits();
+
+    /**
+     * Create a new inventory record (e.g., for finished goods).
+     * 
+     * @param array $data
+     * @return object
+     */
+    public function createInventoryRecord(array $data);
+
+    /**
+     * Decrease quantity of a specific inventory record.
+     * 
+     * @param int $inventoryId
+     * @param float $quantity
+     * @param string|null $reason
+     * @param string|null $referenceType
+     * @param int|string|null $referenceId
+     * @return void
+     */
+    public function decreaseInventoryQuantity(int $inventoryId, float $quantity, ?string $reason = null, ?string $referenceType = null, $referenceId = null);
+}