Implement comprehensive stock management integration (v1.1.0)

Added complete inventory tracking system for composable products:
- Stock validation during product selection and add-to-cart
- Automatic stock deduction on order completion/processing
- Automatic stock restoration on order cancellation/refund
- Stock status indicators with visual feedback (In stock, Low stock, Out of stock)
- Prevention of out-of-stock item selection
- Low stock warnings when 5 or fewer items remain
- Order notes documenting all stock changes

New files:
- includes/Stock_Manager.php: Core stock management logic

Modified files:
- includes/Cart_Handler.php: Integrated stock validation
- includes/Product_Selector.php: Added stock info to product data
- includes/Plugin.php: Added Stock_Manager to includes
- templates/product-selector.twig: Stock status display
- assets/css/frontend.css: Stock indicator styling
- languages/*.pot/*.po: 8 new translatable strings

Version bumped to 1.1.0 with updated CHANGELOG.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

includes/Cart_Handler.php

@@ -15,16 +15,26 @@ defined('ABSPATH') || exit;
  * Handles adding composable products to cart and calculating prices
  */
 class Cart_Handler {
+    /**
+     * Stock manager instance
+     *
+     * @var Stock_Manager
+     */
+    private $stock_manager;
+
     /**
      * Constructor
      */
     public function __construct() {
+        $this->stock_manager = new Stock_Manager();
+
         add_filter('woocommerce_add_to_cart_validation', [$this, 'validate_add_to_cart'], 10, 3);
         add_filter('woocommerce_add_cart_item_data', [$this, 'add_cart_item_data'], 10, 2);
         add_filter('woocommerce_get_cart_item_from_session', [$this, 'get_cart_item_from_session'], 10, 2);
         add_filter('woocommerce_get_item_data', [$this, 'display_cart_item_data'], 10, 2);
         add_action('woocommerce_before_calculate_totals', [$this, 'calculate_cart_item_price']);
         add_action('woocommerce_single_product_summary', [$this, 'render_product_selector'], 25);
+        add_action('woocommerce_checkout_create_order_line_item', [$this->stock_manager, 'store_selected_products_in_order'], 10, 3);
     }
 
     /**
@@ -87,6 +97,13 @@ class Cart_Handler {
             }
         }
 
+        // Validate stock availability
+        $stock_validation = $this->stock_manager->validate_stock_availability($selected_products, $quantity);
+        if ($stock_validation !== true) {
+            wc_add_notice($stock_validation, 'error');
+            return false;
+        }
+
         return $passed;
     }