feat: implement multiple saved addresses with modal selector in checkout

- Add AddressController with full CRUD API for saved addresses
- Implement address management UI in My Account > Addresses
- Add modal-based address selector in checkout (Tokopedia-style)
- Hide checkout forms when saved address is selected
- Add search functionality in address modal
- Auto-select default addresses on page load
- Fix variable products to show 'Select Options' instead of 'Add to Cart'
- Add admin toggle for multiple addresses feature
- Clean up debug logs and fix TypeScript errors

includes/Api/CheckoutController.php

@@ -158,6 +158,37 @@ class CheckoutController {
             return ['error' => $order->get_error_message()];
         }
 
+        // Set customer ID if user is logged in
+        if (is_user_logged_in()) {
+            $user_id = get_current_user_id();
+            $order->set_customer_id($user_id);
+            
+            // Update user's billing information from checkout data
+            if (!empty($payload['billing'])) {
+                $billing = $payload['billing'];
+                
+                // Update first name and last name
+                if (!empty($billing['first_name'])) {
+                    update_user_meta($user_id, 'first_name', sanitize_text_field($billing['first_name']));
+                    update_user_meta($user_id, 'billing_first_name', sanitize_text_field($billing['first_name']));
+                }
+                if (!empty($billing['last_name'])) {
+                    update_user_meta($user_id, 'last_name', sanitize_text_field($billing['last_name']));
+                    update_user_meta($user_id, 'billing_last_name', sanitize_text_field($billing['last_name']));
+                }
+                
+                // Update billing phone
+                if (!empty($billing['phone'])) {
+                    update_user_meta($user_id, 'billing_phone', sanitize_text_field($billing['phone']));
+                }
+                
+                // Update billing email
+                if (!empty($billing['email'])) {
+                    update_user_meta($user_id, 'billing_email', sanitize_email($billing['email']));
+                }
+            }
+        }
+
         // Add items
         foreach ($payload['items'] as $line) {
             $product = $this->load_product($line);
@@ -352,7 +383,7 @@ class CheckoutController {
         if (!WC()->customer) { WC()->customer = new \WC_Customer(get_current_user_id(), true); }
         if (!WC()->cart) { WC()->cart = new \WC_Cart(); }
 
-        // Address context for taxes/shipping rules
+        // Address context for taxes/shipping rules - set temporarily without saving to user profile
         $ship = !empty($payload['shipping']) ? $payload['shipping'] : $payload['billing'];
         if (!empty($payload['billing'])) {
             foreach (['country','state','postcode','city','address_1','address_2'] as $k) {
@@ -370,7 +401,8 @@ class CheckoutController {
                 }
             }
         }
-        WC()->customer->save();
+        // DO NOT save customer data - only use for quote calculation
+        // WC()->customer->save(); // REMOVED - should not update user profile during checkout
 
         WC()->cart->empty_cart(true);
         foreach ($payload['items'] as $line) {