Re-enable the golangci-lint job in CI (disabled Oct 2025), update to
Go 1.25 and golangci-lint-action v7. Fix errcheck, gosimple S1009,
staticcheck SA4031 and SA2001 errors across 54 files. Remaining ~39
lint errors will be addressed in follow-up commits.
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.
