Added a new `/extract-swiss-qr-code` endpoint to extract and parse Swiss QR Codes from the last page of a PDF document. Implemented the `ExtractSwissQrCode` handler method, along with helper methods to map domain value objects (`SwissQrCodeData` and `AddressData`) to DTOs.
Updated `ExceptionHandlingMiddleware` to handle the new `SwissQrCodeNotFoundException` with a 404 Not Found response.
Added integration tests in `ExtractSwissQrCodeEndpointTests` to validate the endpoint's behavior for valid requests, invalid Base64 input, empty references, and empty PDFs. Introduced a helper method to load embedded PDF resources as Base64 strings for testing.
Updated `using` directives to include necessary namespaces for the new feature and exception handling.
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