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.cpp

@@ -0,0 +1,32 @@
+#include "cbt/opengl/descriptor.hpp"
+
+#include "glad/glad.h"
+
+namespace cbt::opengl {
+
+descriptor_set::descriptor_set() {}
+
+auto descriptor_set::add_texture(texture tex, GLuint unit) -> void {
+    m_bindings.push_back({unit, std::move(tex), std::nullopt});
+}
+
+auto descriptor_set::add_buffer(buffer buf, GLuint unit) -> void {
+    m_bindings.push_back({unit, std::nullopt, std::move(buf)});
+}
+
+auto descriptor_set::bind_all() -> void {
+    for (auto& binding : m_bindings) {
+        if (binding.tex) {
+            binding.tex->bind(binding.texture_unit);
+        }
+        if (binding.buf) {
+            binding.buf->bind();
+        }
+    }
+}
+
+auto descriptor_set::count() const -> size_t {
+    return m_bindings.size();
+}
+
+}