Typed customer endpoint responses

Authenticated customer endpoints now return typed profile, cart, order, and course responses.

Authenticated customer storefront endpoints now return typed responses
instead of generic success envelopes. GET, PATCH, and PATCH /password
on /customers/me/profile return customer, store, and
is_generated_password_reset. Cart routes
(GET /customers/me/cart, item add/update/delete) return the customer cart;
cart item add now returns 201. Order routes use the buyer-safe order
response for list and detail responses, with cursor
pagination on the list endpoint. Course routes return typed access, section,
and content responses, plus typed progress update responses.