Frontend: skeleton loading instead of spinners

Spinners hide layout shifts and make an app feel slow even when it isn’t. Skeletons preserve layout and give users a sense of progress without jumping content around. I keep skeleton components simple and match the shape of the final UI. One practical detail: I only show skeletons when loading takes longer than a small threshold (like 150ms) to avoid flashing placeholders on fast connections. It’s a subtle change with a big impact on perceived performance—stable placeholders make the UI feel more polished and trustworthy.