Remove the course's own text from docs/mde once the grade is recorded #354

What

Once the grade for the course project is recorded, remove the course's own text from this repository: docs/mde/assignment.md, docs/mde/practicals.md, and the docs/mde/course-material submodule mount with its .gitmodules entry. Shrink the MDE coursework section of AGENTS.md to a pointer to the reports, and update docs/mde/README.md to match.

The task-0 to task-3 report directories stay, frozen, as design history, as decided on Decide the model-driven implementation's lifespan and sunset.

Acceptance criteria

• npm run verify is green, including lint:links and lint:docs.
• No tracked file links to assignment.md, practicals.md or course-material/.

Blocked by

• The course project grade being recorded (not a ticket).
• Delete the coursework implementation at its sunset (Delete the coursework implementation at its sunset #99)