feat: add RAII window class with OpenGL 4.1 context

- Add cbt::window class in cbt/ directory with RAII lifecycle
- Add setup_opengl and info_opengl for glad init and GL info
- Add Q key to quit the application
- Update CMakeLists.txt with glfw3 and glad dependencies
- Update AGENTS.md with snake_case naming and shell conventions

cbt/window.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <string>
+
+namespace cbt {
+
+class window {
+    void* m_window = nullptr;
+    bool m_initialized = false;
+
+    static auto init() -> bool;
+    static auto terminate() -> void;
+    static auto setup_opengl() -> bool;
+    static auto info_opengl() -> void;
+
+public:
+    explicit window(std::string title, int width, int height);
+    ~window();
+
+    auto should_close() const -> bool;
+    auto valid() const -> bool;
+    auto swap_buffers() -> void;
+    auto poll_events() -> void;
+    auto raw() const -> void* { return m_window; }
+};
+
+}