Fix: course creation - prevent comparison error for books with None for shelf_section

[ascholerChemeketa]

I have a bunch of books in my dev library where shelf_section is None. That crashes the sort code when creating a new course. This fixes the course creation page to handle those.

[Copilot]

Pull request overview

This PR aims to prevent a crash on the course creation page when sorting book shelf_section values that may be None, by introducing a fallback section label.

Changes:

• Default missing shelf_section values to "Misc" when building the sections list for the course creation page.
• Apply the same sections behavior in both the GET handler and the error-rendering path of the POST handler.

Comments suppressed due to low confidence (1)

bases/rsptx/admin_server_api/routers/instructor.py:1450

• Same issue in the error-handling path: sections uses the "Misc" fallback, but course_list retains shelf_section=None, so those books won’t render under any section in the template (it compares course.shelf_section == section). Normalize shelf_section in course_list before computing sections.

        course_list = [c.dict() for c in course_list if c.for_classes]
        sections = sorted({c["shelf_section"] or "Misc" for c in course_list})

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[bnmnetp]

Seems like providing a default for the shelf_section and/or making a pass through course_list to populate None values with Misc would be better so we don't leave books out of the library page.

Also we ought to file issues against those books that don't provide a shelf section so the author can remedy that. I must have "fixed" all those in production a while ago.