Reset scheduling-kit to a truthful package contract for adopter apps and reusable homegrown scheduling.

Completion metrics:

• package UI/payment surfaces no longer inject hidden site policy such as implicit cash fallback
• scheduling-kit ownership is explicit: homegrown backend, shared primitives, generic UI; not the sole owner of Acuity booking flow
• Bazel metadata, package metadata, CI outputs, and published artifacts tell one honest integration story
• downstream apps can validate the intended package artifact before rollout claims are made