Add // stub: unimplemented to 70 empty game-feature handlers and
// stub: reserved to 56 protocol-reserved slots in handlers_reserve.go,
making them discoverable via grep. Add docs/unimplemented.md listing all
unimplemented handlers grouped by subsystem with descriptions.
The userBinary and minidata maps with their locks were spread across
Server as raw fields with manual lock management. Cross-channel session
searches also required acquiring nested locks (server lock + binary
lock). Encapsulating in dedicated types eliminates the nested locking
and reduces Server's field count by 4.
Move time utilities (TimeAdjusted, TimeMidnight, TimeWeekStart, TimeWeekNext,
TimeGameAbsolute) from channelserver into common/gametime to break the
inappropriate dependency where signserver, entranceserver, and api imported
the 38K-line channelserver package just for time functions.
Replace all fmt.Printf debug logging in sys_session.go and handlers_object.go
with structured zap logging for consistent observability.
