Updated documentation and code comments to reflect that the
coordinate system uses INCHES (not 1/100 inch or DX units).
- Updated `COPILOT_CONTEXT_EN.md`:
- Clarified database stores coordinates in INCHES.
- Added conversion formulas and unit comparison table.
- Renamed section to `SignatureDto / AnnotationDto`.
- Updated XML documentation in C# files:
- `SignatureDto.cs`: Added XML comments for INCHES-based coordinates.
- `AnnotationDto.cs`: Corrected unit description and added conversions.
- `AnnotationCreateDto.cs`: Fixed `X` and `Y` property comments.
- Verified VB.NET source (`frmFieldEditor.vb`) as the unit reference.
- Added quick reference for unit conversions across systems.
