Zod v4 migration

[PaulGoldschmidt]

Problem

Currently, MHC uses Zod v3 (^3.25.76). There is Zod v4 available and packages like @stanfordspezi/spezi-firebase-fhir uses already the new version (Zod v4 (^4.0.5).)

Solution

Migrate to Zod v4 once there is enough time.

Additional context

The Zod schemas are completely incompatible and would be in need of a full rewrite.

Code of Conduct

• I agree to follow this project's Code of Conduct and Contributing Guidelines