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

AGENTS.md

@@ -44,6 +44,8 @@ to the custom scripts instead of system-installed packages.
 - `auto` for obvious types (e.g. `auto main(...) -> int`)
 - `<>` includes only for system headers (std, OS, etc.)
 - `""` includes for third-party dependencies (e.g. `fmt`, `nlohmann/json`)
+- **Naming:** `snake_case` for variables, functions, and classes
+- **Naming:** `SCREAMING_SNAKE_CASE` only for macros and constants
 - Include order:
   1. C++ standard library headers (`<chrono>`, `<vector>`, etc.)
   2. *(blank line)*
@@ -86,6 +88,9 @@ Example:
 cuber/
   CMakeLists.txt      # Build configuration
   cuber.cpp           # Entry point
+  cbt/                # Project namespace
+    window.hpp        # Window RAII wrapper
+    window.cpp        # Window implementation
   deps/               # Custom Find*.cmake scripts
     Findfmt.cmake     # fmt library
 ```