Introduced `ISignatureInkPayload` interface to standardize signature ink data and metadata. Updated `DocReceiverElementDto` and `DocReceiverElement` to implement this interface. Enhanced `IPdfPageImageRenderer` with methods for signature preview generation and image format validation.
Replaced `PdfSharp` with `DevExpress` for PDF rendering in `ReceiverSignedPage.razor`. Added `DevSignatureInkController` with endpoints for downloading raw and composed signature images. Updated project files to remove `SixLabors.ImageSharp` and integrate DevExpress.
Added configuration for development endpoints in `appsettings.json`. Improved exception handling, validation, and code maintainability.
