Lemon Squeezy: Connect as a payment provider

Lemon Squeezy is now a fully supported payment provider. Purchases made through Lemon Squeezy automatically create Ghost members, assign labels, and send welcome emails via the same mapping system used for Polar.

• Webhook handler: HMAC-SHA256 signature verification via X-Signature header
• Event mapping: order_created and subscription events translate to Ghost membership actions
• Dashboard connection page: step-by-step setup guide for webhook URL and signing secret
• Product picker: loads Lemon Squeezy products from your store, including test-mode products
• Analytics: webhook events and product mappings visible in the Analytics section