- Move EmailAccountDto.cs to Dtos/ (was in EmailAccounts/ subfolder)
- Move EmailProfileDto.cs to Dtos/ (was in EmailProfiles/ subfolder)
- Keep EmailAttachments/ (3 DTOs) and EmailHistories/ (3 DTOs) subfolders
- Update all namespace imports from Dtos.EmailAccounts/EmailProfiles to Dtos
- Simpler structure: single DTOs at root, multiple DTOs in subfolders