Added full implementation for CreateAnnotationCommand and its handler:
- Introduced `PSPDFKitInstantJSON` property to the command
- Injected repositories for `Signature` and `Annotation`
- Implemented query filtering for Envelope and Receiver
- Added annotation creation from parsed PSPDFKit JSON
- Created helper method `ParsePSPDFKitInstantJSON` for JSON parsing
- Added `UnstructuredAnnotations` property to handle annotations without structured IDs
- Changed default `hasStructuredID` to `False`, set to `True` only after successful parsing
- Updated `AddInstantJSONAnnotationToPDF` to process annotations directly instead of grouping by receiver
- Simplified logic for reversing annotations and applying seal positioning
