feat: add OpenGL abstraction layer with RAII resources

- Replace window class with cbt::opengl::context
- Add buffer resource (VBO, EBO, UBO, SSBO) with move semantics
- Add texture resource with format/type enums and filtering
- Add descriptor_set for Vulkan-style resource binding
- All resources use RAII with proper cleanup

cbt/opengl/descriptor.hpp

@@ -0,0 +1,29 @@
+#pragma once
+
+#include "cbt/opengl/buffer.hpp"
+#include "cbt/opengl/texture.hpp"
+
+#include <array>
+#include <optional>
+#include <vector>
+
+namespace cbt::opengl {
+
+struct descriptor_binding {
+    GLuint texture_unit = 0;
+    std::optional<texture> tex;
+    std::optional<buffer> buf;
+};
+
+class descriptor_set {
+    std::vector<descriptor_binding> m_bindings;
+
+public:
+    descriptor_set();
+    auto add_texture(texture tex, GLuint unit = 0) -> void;
+    auto add_buffer(buffer buf, GLuint unit = 0) -> void;
+    auto bind_all() -> void;
+    auto count() const -> size_t;
+};
+
+}