Several handlers discarded errors from rows.Scan() and db.Exec(),
masking data corruption or connection issues. Scan failures in diva
schedule, event quests, and trend weapons are now logged or returned.
InitializeWarehouse now surfaces its insert error to the caller.
Centralizes all gacha_shop/gacha_entries/gacha_items/gacha_stepup/gacha_box
table access into GachaRepository (15 methods) and all user_binary house
columns, warehouse, and titles table access into HouseRepository (17 methods).
Eliminates all direct DB calls from handlers_gacha.go and handlers_house.go.
