22d2bb1c40
Extract GLFW window management into a dedicated cbt::window class (new files in cbt/). The opengl::context now only handles GLAD setup and context activation (no more window creation or GLFW init/terminate). Updated main loop in cuber.cpp, CMakeLists.txt (to build the new source), and AGENTS.md (docs + source layout). Addresses the design note in context.cpp about mixing concerns.