The day progress bar no longer uses day start/end times (it uses block
durations instead), so the field is no longer needed.
Removed from: Admin UI, schedule store, schedule model/schemas/router,
session broadcast payload, dashboard snapshot, and startup migrations.
DB columns are left in place (harmless, no migration required).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>