The calendar blueprint was nested under calendars (admin), making URLs
/{slug}/admin/{calendar_slug}/ instead of /{slug}/{calendar_slug}/.
Register calendar blueprint directly on the app and update all endpoint
references from calendars.calendar.* to calendar.* (37 in Python,
~50 in templates).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>