- Add IBrandingService interface with ImportLogoAsync, Save/Clear/GetMspLogoAsync
- Add BrandingService: PNG/JPEG magic byte detection, rejects unsupported formats with
descriptive error, auto-compresses files over 512 KB using WPF PresentationCore imaging
- Add BrandingServiceTests: 9 tests covering validation, rejection, compression, CRUD
- Deviation: used WPF BitmapEncoder/TransformedBitmap instead of System.Drawing.Bitmap
(System.Drawing.Common not available without new NuGet package; WPF PresentationCore
is in the existing stack per architectural decisions)