- Add bindAttributeLocation(a_Pos, 0) and bindAttributeLocation(a_Color, 1)
before link() for rendering_program_p_l, rendering_program_line, and
rendering_program_cylinder to guarantee consistent attribute locations
across all OpenGL drivers.
- Remove dead 'in mediump vec4 g_Color[]' from GEOMETRY_SOURCE_LINE_WIDTH
geometry shader (no matching vertex shader output).
- Add proper edge rendering fallback via rendering_program_p_l for
OpenGL < 4.3 where the geometry shader is unavailable.
- Re-add minor version check for OpenGL 4.0-4.2 in qglviewer_impl.h.