feat: add window resize support

Added width/height tracking to the window class via a GLFW
resize callback. The callback stores the current size and
forwards it to a user-provided std::function.

Added context::set_size() to update the GL viewport when
the window is resized.

Changed scene::render() to accept (int width, int height)
parameters so scenes can compute the correct aspect ratio
for their projection matrix instead of hardcoding 1280/720.

Fixed parameter shadowing in resize_callback_impl
(glfw_window instead of window).

cbt/window.cpp

@@ -52,6 +52,12 @@ window::window(std::string title, int width, int height) {
         return;
     }
 
+    m_width = width;
+    m_height = height;
+
+    glfwSetWindowUserPointer(m_window, this);
+    glfwSetWindowSizeCallback(m_window, resize_callback_impl);
+
 #ifdef _WIN32
     auto hwnd = glfwGetWin32Window(m_window);
     BOOL use_dark_mode = TRUE;
@@ -94,6 +100,29 @@ auto window::stop() -> void {
     }
 }
 
+auto window::width() const -> int {
+    return m_width;
+}
+
+auto window::height() const -> int {
+    return m_height;
+}
+
+auto window::on_resize(resize_callback cb) -> void {
+    m_resize_cb = cb;
+}
+
+auto window::resize_callback_impl(GLFWwindow* glfw_window, int width, int height) -> void {
+    auto* self = static_cast<window*>(glfwGetWindowUserPointer(glfw_window));
+    if (self) {
+        self->m_width = width;
+        self->m_height = height;
+        if (self->m_resize_cb) {
+            self->m_resize_cb(width, height);
+        }
+    }
+}
+
 auto window::screenshot(std::string filepath) const -> bool {
     if (!m_window || !valid()) {
         return false;