Add a customer reservation summary with meeting links and iCalendar downloads

Problem/Motivation

Customers need one access-controlled page that explains their reservation, appointment timezone, payment state, and available actions. Meeting links should be accessible after provider synchronization.

Proposed resolution

Add a reservation summary with rescheduling and cancellation actions, Google Meet or Microsoft Teams join links when supplied by the provider, a meeting URL email token, and a private iCalendar download. Do not expose another customer's reservation or management credentials in the calendar file.

Remaining tasks

Implement for the next minor release, add automated coverage, and verify the workflow on a local Drupal site.

Test coverage

Cover customer and anonymous management-link access, unrelated-user denial, provider response parsing, missing and delayed meeting links, iCalendar escaping and line folding, timezone display, and payment states.