Training Type Review

Root Cause

The form uses TanStack Form, not React Hook Form.
trainingType in create mode was initialized as undefined.
The field-level blur validator had already been improved, but the submit-level Zod schema still used z.enum(...).
When submit validation ran with an unset value, Zod could still produce a raw type error path like expected string, received undefined instead of the intended Thai message.

Changed trainingType form default from undefined to "" in create mode.
Kept edit mode bound to the stored UI value.
Updated the Select binding to pass undefined to Radix only for display when the current form value is empty.
Replaced submit-level z.enum(...) validation with string-based validation plus whitelist refinement so the message always stays:
- กรุณาเลือกประเภทการอบรม
Kept the current app enum contract intact:
- INTERNAL_TRAINING
- EXTERNAL_TRAINING
- ONLINE_COURSE
- OJT

Create mode: open new training record form and submit without selecting training type.
Create mode: select each training type option and verify no raw Zod error appears.
Edit mode: open an existing record and confirm the saved type renders correctly in the select.
Edit mode: change the type and submit successfully.
Validation after submit: confirm the Thai message appears instead of Invalid input or expected string, received undefined.
Table/listing: verify training type badges still render correctly in Training Records and review pages.
Server normalization: verify create/update payloads still map correctly to legacy DB values.