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).

cuber.cpp

@@ -57,6 +57,11 @@ auto main(int argc, char const* argv[]) -> int {
         return 1;
     }
 
+    // Wire up resize callback
+    win.on_resize([&ctx](int width, int height) {
+        ctx.set_size(width, height);
+    });
+
     auto cube_scn = cbt::scenes::cube();
     auto sphere_scn = cbt::scenes::sphere();
 
@@ -118,7 +123,7 @@ auto main(int argc, char const* argv[]) -> int {
         prev = now;
 
         active_scene->update(dt);
-        active_scene->render();
+        active_scene->render(win.width(), win.height());
 
         win.swap_buffers();
         win.poll_events();