fix: Newsletter React error #310 and refactor Wishlist module

Newsletter Fix:
- Move all hooks (useQuery, useMutation) before conditional returns
- Add 'enabled' option to useQuery to control when it fetches
- Fixes React error #310: useEffect called conditionally
- Newsletter page now loads without errors at /marketing/newsletter

Wishlist Module Refactoring:
- Create WishlistSettings.php with 8 configurable settings:
  * Enable guest wishlists
  * Wishlist page selector
  * Show in header toggle
  * Enable sharing
  * Back in stock notifications
  * Max items per wishlist
  * Multiple wishlists support
  * Show add to cart button
- Add has_settings flag to wishlist module in ModuleRegistry
- Initialize WishlistSettings in woonoow.php
- Update customer-spa BaseLayout to use isEnabled('wishlist') check
- Wishlist page already has module check (no changes needed)

Files Added (1):
- includes/Modules/WishlistSettings.php

Files Modified (5):
- admin-spa/src/routes/Marketing/Newsletter.tsx
- includes/Core/ModuleRegistry.php
- woonoow.php
- customer-spa/src/layouts/BaseLayout.tsx
- admin-spa/dist/app.js (rebuilt)

Both newsletter and wishlist now follow the same module pattern:
- Settings via schema (no code required)
- Module enable/disable controls feature visibility
- Settings page at /settings/modules/{module_id}
- Consistent user experience

includes/Core/ModuleRegistry.php

@@ -40,6 +40,7 @@ class ModuleRegistry {
                 'category' => 'customers',
                 'icon' => 'heart',
                 'default_enabled' => true,
+                'has_settings' => true,
                 'features' => [
                     __('Save products to wishlist', 'woonoow'),
                     __('Wishlist page', 'woonoow'),