feat: Multiple fixes and features

1. Add allow_custom_avatar toggle to Customer Settings
2. Implement coupon apply/remove in Cart and Checkout pages
3. Update Cart interface with coupons array and discount_total
4. Implement Downloads page to fetch from /account/downloads API

customer-spa/src/lib/cart/api.ts

@@ -109,3 +109,57 @@ export async function fetchCart(): Promise<Cart> {
   const data = await response.json();
   return data;
 }
+
+/**
+ * Apply coupon to cart via API
+ */
+export async function applyCoupon(couponCode: string): Promise<Cart> {
+  const { apiRoot, nonce } = getApiConfig();
+
+  const response = await fetch(`${apiRoot}/cart/apply-coupon`, {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+      'X-WP-Nonce': nonce,
+    },
+    credentials: 'include',
+    body: JSON.stringify({
+      coupon_code: couponCode,
+    }),
+  });
+
+  if (!response.ok) {
+    const errorData = await response.json().catch(() => ({}));
+    throw new Error(errorData.message || 'Failed to apply coupon');
+  }
+
+  const data = await response.json();
+  return data.cart;
+}
+
+/**
+ * Remove coupon from cart via API
+ */
+export async function removeCoupon(couponCode: string): Promise<Cart> {
+  const { apiRoot, nonce } = getApiConfig();
+
+  const response = await fetch(`${apiRoot}/cart/remove-coupon`, {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+      'X-WP-Nonce': nonce,
+    },
+    credentials: 'include',
+    body: JSON.stringify({
+      coupon_code: couponCode,
+    }),
+  });
+
+  if (!response.ok) {
+    const errorData = await response.json().catch(() => ({}));
+    throw new Error(errorData.message || 'Failed to remove coupon');
+  }
+
+  const data = await response.json();
+  return data.cart;
+}