Eliminate the last three direct DB accesses from handler code:
- CharacterRepo.LoadSaveData: replaces db.Query in GetCharacterSaveData,
using QueryRow instead of Query+Next for cleaner single-row access
- EventRepo.GetEventQuests, UpdateEventQuestStartTime, BeginTx: moves
event quest enumeration and rotation queries behind the repo layer
- UserRepo.BanUser: consolidates permanent/temporary ban upserts into a
single method with nil/*time.Time semantics
Centralizes all 31 direct users-table SQL queries from 11 handler
files into a single UserRepository, following the same pattern as
CharacterRepository and GuildRepository. The only excluded query is
the sign_sessions JOIN in handleMsgSysLogin which spans multiple
tables.
