Backend: AccountSession API for Connect embedded components

[windsornguyen]

Create a server-side API endpoint that generates Stripe AccountSession objects for connected accounts. This is the prerequisite for all embedded Connect components on the frontend.

Implementation:

• Endpoint: POST /api/stripe-connect/account-session
• Accepts: connected account ID
• Returns: client_secret for frontend ConnectComponentsProvider
• Must enable components: account_onboarding, account_management, payments, payouts, balances, documents, payment_details

const accountSession = await stripe.accountSessions.create({
  account: 'acct_xxx',
  components: {
    payouts: { enabled: true },
    payments: { enabled: true },
    balances: { enabled: true },
    account_onboarding: { enabled: true },
    account_management: { enabled: true },
    documents: { enabled: true },
    payment_details: { enabled: true, features: { refund_management: true } },
  },
});

Collaborator: @anny — backend lead for marketplace