Improve error handling for GraphQL mutations in the Mentorship Portal

**Describe the bug**
When errors come from the backend during Program or Module create/update actions, they are returned as generic GraphQL errors without enough structure. Because of this, the frontend cannot reliably understand whether the error is related to validation, permissions, or something else, which leads to unclear feedback for users.

**Expected behavior**
Backend errors should be returned in a structured and consistent way so the frontend can properly display meaningful messages to users.

**Are you going to work on fixing this?**

- [x] Yes
- [ ] No

**Additional context**
Although the frontend already has some validation, it still depends on clear and structured error responses from the backend to handle edge cases