The admin dashboard and instructor My Lessons pages showed the raw
availability-slot database ID, which is meaningless to admins and
instructors. LessonController now takes AvailabilityRepository, looks up
each lesson's slot, and renders its window as e.g.
"Jul 6, 2026 9:00 AM-10:00 AM" via mysql2date. The date is repeated on
the end time only when a slot crosses midnight, and lessons whose slot
row no longer exists show an em dash.
Closes#47
Co-Authored-By: Claude Fable 5 <[email protected]>
