feat(calendar): show a descriptive name in ICS subscription feeds

Add per-subscription calendar name (schedule name, resource name,
resource group name, or the current user's own calendar) and pass it
to CalendarExportDisplay::Render() so subscribed calendars ics files
get a readable NAME/X-WR-CALNAME instead of a generic one in calendar
clients.

Assisted-by: Claude:claude-sonnet-5