Chemistry QPE course tracking issue

This issue tracks follow-up work identified while reviewing the Chemistry QPE course in #3568.

- [x] "Start learning" is slow, and switching courses before it finishes redirects the learner to katas instead of the chosen course.
- [ ] Notify user if they are using the old workspace with older course content
- [ ] Keep generated notebook cell IDs stable when cell content changes.
- [x] Find `course.json` without searching parent directories.
- [ ] Check the installed QDK/Chemistry version as part of environment validation.
- [ ] Decide whether output baking should remain Chemistry-specific or become shared course tooling.
- [ ] Improve exercises so hard coded answers do not pass.
- [ ] Require exercise checkers to run before an exercise is completed.
- [ ] Investigate notebook save prompts when auto save is enabled.
- [x] Preserve or reapply the selected python kernel across units.
- [x] Investigate notebook freezing while switching units or kernels.
- [ ] Explore a Copilot action for prose quiz questions. (stale if custom mime type quizzes take place)
- [x] An authoring guide for the authors to create QDK Python learning courses
- [x] Convert PNGs to SVGs

Start with the Chemistry QPE course review in issue #3568 and use the unchecked checklist in this issue as the scope. Inspect the course.json lookup and the QDK Python course and notebook tooling mentioned there; completion requires resolving or explicitly deciding each remaining item, with validation for the affected course workflows.

Written by the indexing model from the issue text.