refactor(channelserver): move remaining s.server.db calls into repositories

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

server/channelserver/repo_mocks_test.go

@@ -194,6 +194,7 @@ func (m *mockCharacterRepo) UpdateGCPAndPact(_ uint32, _ uint32, _ uint32) error
 func (m *mockCharacterRepo) FindByRastaID(_ int) (uint32, string, error)                         { return 0, "", nil }
 func (m *mockCharacterRepo) SaveCharacterData(_ uint32, _ []byte, _, _ uint16, _ bool, _ uint8, _ uint16) error { return nil }
 func (m *mockCharacterRepo) SaveHouseData(_ uint32, _ []byte, _, _, _, _, _ []byte) error        { return nil }
+func (m *mockCharacterRepo) LoadSaveData(_ uint32) (uint32, []byte, bool, string, error)         { return 0, nil, false, "", nil }
 
 // --- mockGoocooRepo ---