Stripe Payment Integration Stripe payment extension for Caffeine AI. Overview This skill adds Stripe payment support using HTTP outcalls. The mixin provides configuration, checkout session creation, payment status checks, and the HTTP outcall callback. The frontend handles checkout flow and payment result pages. Inbound Stripe webhooks (an external to the canister) are not covered here — use for the / handlers, then verify Stripe signatures in the update path. Prerequisite: You must follow extension-authorization first, as this integration depends on it. Backend Module API The prefabricated m…