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

deps/Findglad.cmake

@@ -0,0 +1,68 @@
+# ==============================================================================
+# Find glad
+# ==============================================================================
+# This module fetches the glad OpenGL loader library.
+#
+# Targets provided:
+#   glad::glad - The glad library target
+#
+# Variables set:
+#   glad_FOUND       - TRUE if glad is available
+#   glad_LIBRARIES   - The glad library target (glad::glad)
+#   glad_INCLUDE_DIR - Include directories for glad
+#   glad_VERSION     - Version of glad (commit hash or tag)
+# ==============================================================================
+
+if (DEFINED _FINDGLAD_INCLUDED)
+    return()
+endif()
+set(_FINDGLAD_INCLUDED TRUE)
+
+# Use the version passed to find_package(), or default to commit hash
+if (DEFINED glad_FIND_VERSION AND NOT glad_FIND_VERSION STREQUAL "")
+    set(GLAD_VERSION "${glad_FIND_VERSION}")
+else()
+    set(GLAD_VERSION "f4759d7c5143c0a23391ab05caaf43052cefdd65")
+endif()
+
+message(STATUS "Fetching glad ${GLAD_VERSION}")
+
+include(FetchContent)
+
+find_program(GIT_EXECUTABLE git)
+if (GIT_EXECUTABLE)
+    set(GLAD_FETCH_METHOD "GIT")
+else()
+    message(FATAL_ERROR "Fetch with zip not supported.")
+endif()
+
+if (GLAD_FETCH_METHOD STREQUAL "GIT")
+    FetchContent_Declare(
+        glad
+        GIT_REPOSITORY https://github.com/mononerv/glad.git
+        GIT_TAG        ${GLAD_VERSION}
+    )
+endif()
+
+FetchContent_MakeAvailable(glad)
+
+if (NOT TARGET glad::glad)
+    if (TARGET glad)
+        add_library(glad::glad ALIAS glad)
+    else()
+        message(FATAL_ERROR "Could not fetch glad; no target glad or glad::glad available")
+    endif()
+endif()
+
+set(glad_FOUND        TRUE)
+set(glad_LIBRARIES    glad::glad)
+set(glad_VERSION      "${GLAD_VERSION}")
+get_target_property(_glad_inc glad::glad INTERFACE_INCLUDE_DIRECTORIES)
+set(glad_INCLUDE_DIR  "${_glad_inc}")
+
+# Mark glad includes as SYSTEM to suppress warnings from its headers
+if (_glad_inc AND TARGET glad)
+    set_target_properties(glad PROPERTIES
+        INTERFACE_SYSTEM_INCLUDE_DIRECTORIES "${_glad_inc}"
+    )
+endif()