- Allow users to select a transparent color for logo images (watermarks) via UI (checkbox, color picker, preview).
- Apply color-key transparency in both System.Drawing and ImageSharp backends: specified color in logo is made fully transparent.
- Persist transparency settings in PicSettings and SettingsDto; bind to DataModel and UI controls.
- Update logo preview to reflect transparency in real time.
- Add option to select image processing library (System.Drawing or ImageSharp) in UI and settings.
- Fix bug in SettingsService parameter loading for int/double/DateTime.
- Fully integrate color-key transparency into image processing and settings serialization.
