Stripe ⇄ Discord

Server läuft.

• POST /create-checkout-session {"priceId":"price_..."} (optional mit ?survey=1&token=...)
• /success?session_id=... führt zur Discord-Verknüpfung
• n8n Endpoints: POST /internal/discord/grant | /internal/discord/revoke
• Stripe Webhook: POST /webhooks/stripe