fix(helcim): skip HelcimPay verify when a card is already on file

Helcim refuses paymentType:'verify' for cards already saved on a
customer ("A new card must be entered for saving the payment method"),
breaking every "Complete Payment" retry after a partial-failed signup.

Add GET /api/helcim/existing-card and short-circuit HelcimPay verify in
useMemberPayment + payment-setup.vue when a saved card is found, going
straight to subscription creation. The two existence-check fetches run
in parallel with get-or-create-customer so no extra round-trip latency
in the common path.

app/composables/useMemberPayment.js

@@ -25,45 +25,53 @@ export const useMemberPayment = () => {
     paymentSuccess.value = false
 
     try {
-      // Step 1: Get or create Helcim customer
-      await getOrCreateCustomer()
+      // Skip HelcimPay verify if a card's already on file — Helcim refuses
+      // to re-save it, breaking retries after a partial-failed signup.
+      const [, existing] = await Promise.all([
+        getOrCreateCustomer(),
+        $fetch('/api/helcim/existing-card').catch((err) => {
+          console.warn('[payment] existing-card lookup failed, falling back to verify flow:', err)
+          return null
+        }),
+      ])
 
-      // Step 2: Initialize Helcim payment with $0 for card verification
-      await initializeHelcimPay(
-        customerId.value,
-        customerCode.value,
-        0,
-      )
+      let cardToken = existing?.cardToken || null
 
-      // Step 3: Show payment modal and get payment result
-      const paymentResult = await verifyPayment()
-      console.log('Payment result:', paymentResult)
+      if (!cardToken) {
+        await initializeHelcimPay(
+          customerId.value,
+          customerCode.value,
+          0,
+        )
 
-      if (!paymentResult.success) {
-        throw new Error('Payment verification failed')
+        const paymentResult = await verifyPayment()
+
+        if (!paymentResult.success) {
+          throw new Error('Payment verification failed')
+        }
+
+        const verifyResult = await $fetch('/api/helcim/verify-payment', {
+          method: 'POST',
+          body: {
+            cardToken: paymentResult.cardToken,
+            customerId: customerId.value,
+          },
+        })
+
+        if (!verifyResult.success) {
+          throw new Error('Payment verification failed on backend')
+        }
+
+        cardToken = paymentResult.cardToken
       }
 
-      // Step 4: Verify payment on backend
-      const verifyResult = await $fetch('/api/helcim/verify-payment', {
-        method: 'POST',
-        body: {
-          cardToken: paymentResult.cardToken,
-          customerId: customerId.value,
-        },
-      })
-
-      if (!verifyResult.success) {
-        throw new Error('Payment verification failed on backend')
-      }
-
-      // Step 5: Create subscription with proper contribution tier
       const subscriptionResponse = await $fetch('/api/helcim/subscription', {
         method: 'POST',
         body: {
           customerId: customerId.value,
           customerCode: customerCode.value,
           contributionAmount: memberData.value?.contributionAmount ?? 5,
-          cardToken: paymentResult.cardToken,
+          cardToken,
         },
       })
 
@@ -71,7 +79,6 @@ export const useMemberPayment = () => {
         throw new Error('Subscription creation failed')
       }
 
-      // Step 6: Payment successful - refresh member data
       paymentSuccess.value = true
       await checkMemberStatus()