[Bug]: Add more error handling in planner page

[mhd-hi]

What happened?

When database or backend is down, we only send a toast saying something like "Internal Server Error".

What is the expected behaviour?

We also to add a clear message that we couldnt find any programs when user tries to search for a program, or a course.

So :

• Add toast in Programs selector
• Add toast in CoursesList

Steps to reproduce

You can stop the backend (locally ofc)

Screenshots and additional context

No response