Update billing schema and plan picker logic

Modified the logic in create-billing-schema.ts so if a plan contains more than one line item, it no longer returns true but false. In plan-picker.tsx, added a condition to check if a product is selected before setting the 'planId'. Also, the 'planId' is now set based on the selected plan's id rather than an empty string.

packages/billing/core/src/create-billing-schema.ts

@@ -215,13 +215,13 @@ const BillingSchema = z
         for (const product of schema.products) {
           for (const plan of product.plans) {
             if (plan.lineItems.length > 1) {
-              return true;
+              return false;
+            }
           }
         }
       }
 
       return true;
-      }
     },
     {
       message: 'Lemon Squeezy only supports one line item per plan',

packages/billing/gateway/src/components/plan-picker.tsx

@@ -15,6 +15,7 @@ import {
   getPrimaryLineItem,
   getProductPlanPair,
 } from '@kit/billing';
+import config from '@kit/prettier-config/index.mjs';
 import { formatCurrency } from '@kit/shared/utils';
 import { Badge } from '@kit/ui/badge';
 import { Button } from '@kit/ui/button';
@@ -153,13 +154,15 @@ export function PlanPicker(
                                   id={interval}
                                   value={interval}
                                   onClick={() => {
-                                    form.setValue('planId', '', {
+                                    if (selectedProduct) {
-                                      shouldValidate: true,
+                                      const plan = selectedProduct.plans.find(
-                                    });
+                                        (item) => item.interval === interval,
+                                      );
 
-                                    form.setValue('productId', '', {
+                                      form.setValue('planId', plan?.id ?? '', {
                                         shouldValidate: true,
                                       });
+                                    }
 
                                     form.setValue('interval', interval, {
                                       shouldValidate: true,