feat: Add-to-cart from URL parameters

Implements direct-to-cart functionality for landing page CTAs.

Features:
- Parse URL parameters: ?add-to-cart=123
- Support simple products: ?add-to-cart=123
- Support variable products: ?add-to-cart=123&variation_id=456
- Support quantity: ?add-to-cart=123&quantity=2
- Auto-navigate to cart after adding
- Clean URL after adding (remove parameters)
- Toast notification on success/error

Usage examples:
1. Simple product:
   https://site.com/store?add-to-cart=332

2. Variable product:
   https://site.com/store?add-to-cart=332&variation_id=456

3. With quantity:
   https://site.com/store?add-to-cart=332&quantity=3

Flow:
- User clicks CTA on landing page
- Redirects to SPA with add-to-cart parameter
- SPA loads, hook detects parameter
- Adds product to cart via API
- Navigates to cart page
- Shows success toast

Works with both SPA modes:
- Full SPA: loads shop, adds to cart, navigates to cart
- Checkout Only: loads cart, adds to cart, stays on cart

templates/spa-full-page.php

@@ -12,15 +12,21 @@
     $appearance_settings = get_option('woonoow_appearance_settings', []);
     $spa_mode = isset($appearance_settings['general']['spa_mode']) ? $appearance_settings['general']['spa_mode'] : 'full';
     
+    // Debug logging
+    error_log('[WooNooW SPA Template] Settings: ' . print_r($appearance_settings, true));
+    error_log('[WooNooW SPA Template] SPA Mode: ' . $spa_mode);
+    
     // Set initial page based on mode
     if ($spa_mode === 'checkout_only') {
         // Checkout Only mode starts at cart
         $page_type = 'cart';
         $data_attrs = 'data-page="cart" data-initial-route="/cart"';
+        error_log('[WooNooW SPA Template] Using CART initial route');
     } else {
         // Full SPA mode starts at shop
         $page_type = 'shop';
         $data_attrs = 'data-page="shop" data-initial-route="/shop"';
+        error_log('[WooNooW SPA Template] Using SHOP initial route');
     }
     ?>