Polish publication readiness

[bofandra]

Summary

Prepare the repository for a stable public course release without changing learning outcomes or assessment scope.

Changes

• add a concise Course at a glance section to the landing README;
• separate learner resources from facilitator/maintainer resources;
• add PUBLICATION_CHECKLIST.md with recommended repository description, topics, versioning, and release checks;
• add RELEASE_NOTES.md as the prepared v1.0.0 candidate release body;
• extend course validation so publication/release assets remain present and linked;
• document the publication-readiness work in CHANGELOG.md.

Not changed

• Module 0–16 curriculum;
• formal references;
• assessment model;
• source-boundary policy.