refactor: separate window from opengl::context

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.

cbt/opengl/context.cpp

@@ -1,18 +1,8 @@
 #include <string_view>
 
-#ifdef _WIN32
-#include <dwmapi.h>
-#include <windows.h>
-#endif
-
 #define GLFW_INCLUDE_NONE
 #include "GLFW/glfw3.h"
 
-#ifdef _WIN32
-#define GLFW_EXPOSE_NATIVE_WIN32
-#include "GLFW/glfw3native.h"
-#endif
-
 #include "fmt/std.h"
 #include "glad/glad.h"
 
@@ -20,18 +10,6 @@
 
 namespace cbt::opengl {
 
-auto context::init() -> bool {
-    if (!glfwInit()) {
-        fmt::print("Failed to initialize GLFW\n");
-        return false;
-    }
-    return true;
-}
-
-auto context::terminate() -> void {
-    glfwTerminate();
-}
-
 auto context::setup_gl() -> bool {
     if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
         fmt::print("Failed to initialize GLAD\n");
@@ -50,64 +28,18 @@ auto context::print_info() -> void {
     fmt::print("\n");
 }
 
-context::context(std::string title, int width, int height) {
-    if (!init()) {
-        return;
-    }
-    m_initialized = true;
-
-    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
-    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 1);
-    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
-
-    m_window = glfwCreateWindow(width, height, title.c_str(), nullptr, nullptr);
-    if (!m_window) {
-        fmt::print("Failed to create window\n");
-        terminate();
-        return;
-    }
-
-    glfwMakeContextCurrent(m_window);
-
-#ifdef _WIN32
-    auto hwnd = glfwGetWin32Window(static_cast<GLFWwindow*>(m_window));
-    BOOL use_dark_mode = TRUE;
-    DwmSetWindowAttribute(hwnd, DWMWA_USE_IMMERSIVE_DARK_MODE, &use_dark_mode, sizeof(use_dark_mode));
-#endif
-
+context::context(window const& win) {
+    glfwMakeContextCurrent(win.raw());
     if (!setup_gl()) {
-        terminate();
         return;
     }
+    m_valid = true;
 }
 
-context::~context() {
-    if (m_window) {
-        glfwDestroyWindow(m_window);
-    }
-    if (m_initialized) {
-        terminate();
-    }
-}
-
-auto context::should_close() const -> bool {
-    return m_window && glfwWindowShouldClose(m_window);
-}
+context::~context() {}
 
 auto context::valid() const -> bool {
-    return m_window != nullptr;
-}
-
-auto context::swap_buffers() -> void {
-    glfwSwapBuffers(m_window);
-}
-
-auto context::poll_events() -> void {
-    glfwPollEvents();
-}
-
-auto context::raw() const -> GLFWwindow* {
-    return m_window;
+    return m_valid;
 }
 
 }