Площадь, угол, сохранение проекта и таблица измерений
- Added project Save / Load as JSON, so measurements can be continued later.
- Added polygon Area measurement for closed shapes and surface calculations.
- Added Angle measurement for two connected lines with shared endpoints.
- Added an optional Measurements table with editable names and CSV export.
- Improved exports so PNG, JPG, and PDF include the new measurement types.