Introduced a new `SignatureCaptureDto` model to encapsulate
signature-related data and metadata, replacing the previous
`SignatureCapture` type in `EnvelopeViewer.razor`.
- Added `SignatureCaptureDto` in `SignatureCaptureDto.cs` with
properties for signature image, signer name, position, and place.
- Updated `_capturedSignature` to use `SignatureCaptureDto` for
consistency and maintainability.
- Refactored signature capture logic to initialize
`SignatureCaptureDto` using object initializer syntax.
- Improved code clarity with detailed XML documentation for
`SignatureCaptureDto`.
These changes enhance maintainability, readability, and ensure
a centralized model for signature-related data.
