[215_7] fix ellipse array bounds issue (#2944)

[physical168]

No description provided.

[physical168]

This PR addresses the crash issue when interacting with ellipses in drawing mode (#2944).

Problem:
ellipse_rep::get_control_points returned 3 control points, but initialized the abs array with only 2 values. This led to out-of-bounds access during graphical selection.

Solution:
Aligned the abs array size to 3 with values 0.0, 0.5, 1.0 to match the control point count.

Details:

• Modified src/Graphics/Types/curve.cpp
• Added developer documentation at devel/215_7.md

[JackYansongLi]

Please format your code with Clang@19.

[physical168]

Thanks for reviewing my code! I've just reformatted the code using Clang and pushed the update. Please check if it complies with the project's style.