add company stamp upload functionality for contract signing

- Introduced StampUpload component for uploading company stamp images.
- Integrated stamp upload in contract signing modal, supporting PNG and JPG formats.
- Implemented validation for file type and size (max 5 MB).
- Added visual feedback for drag-and-drop functionality.
- Updated contract-related pages to handle duplicate contract alerts and pricing notices.
- Enhanced contract expiry management with a nightly sweep service.
- Added unit tests for new features and updated existing tests for contract handling.

apps/edr-freight-api/src/modules/contracts/dto/sign-contract.dto.ts

@@ -17,6 +17,17 @@ export class SignContractDto {
   @MinLength(20)
   signatureImageBase64?: string;
 
+  @ApiPropertyOptional({
+    description:
+      'PNG company stamp/seal image as base64 (with or without data URL prefix). ' +
+      'Required for the CUSTOMER and STAFF roles — both parties must seal the ' +
+      'contract before it is fully executed.',
+  })
+  @IsOptional()
+  @IsString()
+  @MinLength(20)
+  stampImageBase64?: string;
+
   @ApiProperty()
   @IsString()
   @MinLength(1)