- createRequestSchema now requires employee_id to be a UUID-format
string (was a free-text non-empty check), matching the new FK to
Employee in schema.prisma.
- createRequest() now returns a CreateRequestResult discriminated
union and catches Prisma P2003 (FK violation), returning a friendly
ok:false error instead of a raw 500 when employee_id does not
reference an existing Employee. POST /api/requests branches on
created.ok and returns 400 in that case.
- tests/requests.test.ts: every test that used to POST a fake string
employee_id (emp-1, emp-2) now creates a real Employee first via
createTestEmployee() and uses its id, since employee_id is now a
real FK. Added coverage for a syntactically invalid UUID and for a
well-formed but non-existent UUID (expects the friendly 400 from
the P2003 catch, not a raw 500) - the exact case this retrofit was
meant to protect against.