fix(account): show payment history + next-charge for paid-then-$0 members

Three related changes on /member/account:

1. Payment History section now renders when contributionAmount > 0 OR
   past payments exist. Previously a paid member who switched to $0 lost
   visibility of their own past charges.

2. New "Next charge: $X on DATE" row renders above the transaction list
   when nextPaymentDate is available, using --candle dashed border.

3. server/api/helcim/subscription.get.js now reads dateBilling from
   Helcim's GET response and handles data as either object or array.
   Helcim's real shape is {data: {id, dateBilling, ...}} — the old code
   expected {data: [{nextBillingDate}]} and returned empty strings, so
   the Membership-card "Next payment" row never rendered for members
   whose cached date was missing. subscription.post.js and
   update-contribution.post.js have the same wrong field name in their
   CREATE flows; left for a follow-up — the GET refresh masks it.

Manual edit-flow and admin-flow tests also recorded in
docs/LAUNCH_READINESS.md.

server/api/helcim/subscription.get.js

@@ -19,11 +19,15 @@ export default defineEventHandler(async (event) => {
 
   try {
     const response = await getHelcimSubscription(member.helcimSubscriptionId)
-    const subscription = Array.isArray(response)
-      ? response[0]
-      : (response?.data?.[0] || response)
+    const data = response?.data
+    const subscription = Array.isArray(data)
+      ? data[0]
+      : (data && typeof data === 'object' ? data : response)
 
-    const nextBillingDate = subscription?.nextBillingDate || null
+    // Helcim's GET /subscriptions/:id returns `dateBilling` (YYYY-MM-DD).
+    // POST /subscriptions responses have sometimes been seen with `nextBillingDate`;
+    // accept both so the refresh works regardless of shape.
+    const nextBillingDate = subscription?.dateBilling || subscription?.nextBillingDate || null
 
     if (nextBillingDate) {
       const parsed = new Date(nextBillingDate)