Introduce mesh3d_hair GLSL shaders with alpha-blended Vulkan pipeline (no back-face cull, depth write disabled). Expose gfx.newHairShader(), Renderable3D.setHair() for a back-to-front transparent pass in RenderSystem3D, plus HairShader helpers and unit tests. Co-authored-by: Cursor Agent <cursoragent@cursor.com>