degree requirements: serve via rest api for schedulelab

[jaspermayone]

Depends on #526.

Expose degree requirements to ScheduleLab over REST. GraphQL is ruled out.

Agreed flow (call, 2026-08-13)

• The user grants access through an OAuth-style permission screen in ScheduleLab.
• We match the user on their .edu email. We do not store W numbers.
• After the grant, we return the user's previous registrations plus the requirements for their major and catalog year.
• ScheduleLab can also request requirements by major + catalog year alone (they have no accounts yet).

Tasks

• Endpoint: requirements by degree program + catalog year.
• Auth: API credentials for ScheduleLab plus the per-user grant flow.
• Document the request and response format for Jordan.

Meeting notes: https://notes.granola.ai/t/6aa6ed59-eaad-4cea-86cd-1fcb7c327f89-00demib2