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

admin-spa/src/routes/Appearance/General.tsx

@@ -76,11 +76,16 @@ export default function AppearanceGeneral() {
         
         // Load available pages
         const pagesResponse = await api.get('/pages/list');
-        if (pagesResponse.data?.data) {
-          setAvailablePages(pagesResponse.data.data);
+        console.log('Pages API response:', pagesResponse);
+        if (pagesResponse.data) {
+          console.log('Pages loaded:', pagesResponse.data);
+          setAvailablePages(pagesResponse.data);
+        } else {
+          console.warn('No pages data in response:', pagesResponse);
         }
       } catch (error) {
         console.error('Failed to load settings:', error);
+        console.error('Error details:', error);
       } finally {
         setLoading(false);
       }