Players could never claim monthly guild items because the handler
always returned 0x01 (claimed). Now tracks per-character per-type
(standard/HLC/EXC) claim timestamps in the stamps table, comparing
against the current month boundary to determine claim eligibility.
Adds MonthStart() to gametime, extends StampRepo with
GetMonthlyClaimed/SetMonthlyClaimed, and includes schema migration
31-monthly-items.sql.
Add package-level documentation (doc.go) to all 22 first-party
packages and godoc comments to ~150 previously undocumented
exported symbols across common/, network/, and server/.
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.
