Move scan loops from handlers into repository methods so that interfaces
return typed slices instead of leaking database cursors. This fixes
resource leaks (7 of 12 call sites never closed rows) and makes all
12 methods mockable for unit tests.
Affected repos: CafeRepo, ShopRepo, EventRepo, RengokuRepo, DivaRepo,
ScenarioRepo, MiscRepo, MercenaryRepo. New structs: DivaEvent,
MercenaryLoan, GuildHuntCatUsage. EventRepo.GetEventQuests left as-is
(requires broader Server refactor).
Move all direct DB access from handlers_rengoku.go (11 calls) and
handlers_mail.go (10 calls) into dedicated repository types, continuing
the established extraction pattern.
RengokuRepository provides UpsertScore and GetRanking, replacing a
3-call check/insert/update sequence and an 8-case switch of nearly
identical queries respectively.
MailRepository provides SendMail, SendMailTx, GetListForCharacter,
GetByID, MarkRead, MarkDeleted, SetLocked, and MarkItemReceived.
The old Mail.Send(), Mail.MarkRead(), GetMailListForCharacter, and
GetMailByID free functions are removed. Guild handlers that sent mail
via Mail.Send(s, ...) now call mailRepo directly.
