Move the "all-time" constant out of GameCalendarService (concrete) into a new
static class GameCalendarPeriods. Consumers using IGameCalendarService no
longer have to reach through the concrete class to name the lifetime bucket.
Migrates 5 callsites (mission progress/assembler, admin, item purchase, tests).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>