Add readCharacterInt/adjustCharacterInt helpers for single-column
integer operations on the characters table. Eliminates fmt.Sprintf
SQL construction in handlers_misc.go and replaces inline queries
across cafe, kouryou, and mercenary handlers.
Second round of protocol constant extraction: adds constants_time.go
(secsPerDay, secsPerWeek), constants_raviente.go (register IDs,
semaphore constants), and named constants across 14 handler files
replacing raw hex/numeric literals. Updates anti-patterns doc to
mark #4 (magic numbers) as substantially fixed.
A malicious or buggy client could send arbitrarily large payloads
that get written directly to PostgreSQL, wasting disk and memory.
Each save handler now rejects payloads exceeding a generous upper
bound derived from the known data format sizes.
Covers all remaining items from #158: partner, hunternavi,
savemercenary, scenariodata, platedata, platebox, platemyset,
rengokudata, mezfes, savefavoritequest, house_furniture, mission.
Closes#158
