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/texture.cpp

@@ -0,0 +1,85 @@
+#include "cbt/opengl/texture.hpp"
+
+#include "glad/glad.h"
+
+namespace cbt::opengl {
+
+texture::texture() {
+    glGenTextures(1, &m_id);
+}
+
+texture::texture(texture_target target)
+    : m_target(target) {
+    glGenTextures(1, &m_id);
+}
+
+texture::~texture() {
+    if (m_id) {
+        glDeleteTextures(1, &m_id);
+    }
+}
+
+texture::texture(texture&& other) noexcept
+    : m_id(other.m_id)
+    , m_target(other.m_target) {
+    other.m_id = 0;
+}
+
+texture& texture::operator=(texture&& other) noexcept {
+    if (this != &other) {
+        if (m_id) {
+            glDeleteTextures(1, &m_id);
+        }
+        m_id = other.m_id;
+        m_target = other.m_target;
+        other.m_id = 0;
+    }
+    return *this;
+}
+
+auto texture::bind(GLuint unit) -> void {
+    glActiveTexture(GL_TEXTURE0 + unit);
+    glBindTexture(static_cast<GLenum>(m_target), m_id);
+}
+
+auto texture::unbind() -> void {
+    glBindTexture(static_cast<GLenum>(m_target), 0);
+}
+
+auto texture::upload(const void* data, int width, int height, texture_format format, texture_type type) -> void {
+    bind();
+    glTexImage2D(static_cast<GLenum>(m_target), 0,
+                 static_cast<GLenum>(format), width, height, 0,
+                 static_cast<GLenum>(format), static_cast<GLenum>(type), data);
+    unbind();
+}
+
+auto texture::set_filter(GLenum min_filter, GLenum mag_filter) -> void {
+    bind();
+    glTexParameteri(static_cast<GLenum>(m_target), GL_TEXTURE_MIN_FILTER, min_filter);
+    glTexParameteri(static_cast<GLenum>(m_target), GL_TEXTURE_MAG_FILTER, mag_filter);
+    unbind();
+}
+
+auto texture::set_wrap(GLenum wrap_s, GLenum wrap_t) -> void {
+    bind();
+    glTexParameteri(static_cast<GLenum>(m_target), GL_TEXTURE_WRAP_S, wrap_s);
+    glTexParameteri(static_cast<GLenum>(m_target), GL_TEXTURE_WRAP_T, wrap_t);
+    unbind();
+}
+
+auto texture::generate_mipmaps() -> void {
+    bind();
+    glGenerateMipmap(static_cast<GLenum>(m_target));
+    unbind();
+}
+
+auto texture::id() const -> GLuint {
+    return m_id;
+}
+
+auto texture::valid() const -> bool {
+    return m_id != 0;
+}
+
+}