fix(auth): expose helcimCustomerId on /api/auth/member

The member account page gates the Helcim customer portal link on
`memberData.helcimCustomerId`, but this endpoint (the source for
`useAuth().memberData`) omitted the field, so the link hid for every
member regardless of Helcim enrollment. Add the field to the response.

server/api/auth/member.get.js

@@ -13,6 +13,7 @@ export default defineEventHandler(async (event) => {
     circle: member.circle,
     contributionTier: member.contributionTier,
     billingCadence: member.billingCadence,
+    helcimCustomerId: member.helcimCustomerId,
     membershipLevel: `${member.circle}-${member.contributionTier}`,
     // Profile fields
     pronouns: member.pronouns,