Changed the `Page` property from `int?` to `int` to ensure it always has a value. Similarly, changed the `X` and `Y` properties from `double?` to `double` to enforce non-nullable values for horizontal and vertical positions.
Added `AnnotationDto` to represent signature annotation positions,
including properties for ID, page, and coordinates, with detailed
documentation on coordinate systems. Implemented `AnnotationService`
to fetch annotation data from an API endpoint, using `HttpClient`
and supporting cancellation tokens. Registered `AnnotationService`
in the DI container to enable its use across the application.
Provided development setup details for working with fake data
via YARP-proxied routes.
