v0.5.1 — display_name in /tutor-status and /tutor-resume

Consistency follow-up to v0.5.0: the statusline already rendered the human display name, but the dashboard and resume orientation kept showing the kebab-cased slug. This release closes the gap.

Behaviour

• /tutor-status shows human topic names. The dashboard's Active and Completed sections now render the subject you typed at /tutor-start instead of the slug-key. So if you started with /tutor-start "Python decorators", the dashboard reads Python decorators, not python-decorators.
• /tutor-resume does the same. The orientation line is now "Resuming Python decorators." When you have multiple active topics, the disambiguation prompt lists them by display name, and you can type the name (or a substring) to pick — no need to recall the exact slug.

Backward compatible: topics created before v0.5.0 don't have a display_name and continue to render as their slug-key. No migration needed.