Fix errcheck violations across 11 repo files by wrapping deferred
rows.Close() and tx.Rollback() calls to discard the error return.
Fix unchecked Scan/Exec calls in guild store tests. Fix staticcheck
SA9003 empty branch in test helpers.
Add 6 mock-based unit tests for GetCharacterSaveData covering nil
savedata, sql.ErrNoRows, DB errors, compressed round-trip,
new-character skip, and config mode/pointer propagation.
Eliminate 18 direct s.server.db calls from handlers_items.go,
handlers_distitem.go, and handlers_session.go by moving queries into
dedicated repository types.
New repositories:
- StampRepository (7 methods, stamps table)
- DistributionRepository (4 methods, distribution/distribution_items)
- SessionRepository (4 methods, sign_sessions/servers)
Also adds ClearTreasureHunt and InsertKillLog to GuildRepository,
which already owns those tables for read operations.
