add popup animation

[hwhmeikle]

New Features

• Popup animations — smooth fade and scale animation when the popup opens and closes
• Loading state — the popup iframe is hidden until content is ready, eliminating the blank white flash during load
• Reduced motion support — animations are automatically disabled when the user prefers reduced motion

Bug Fixes

• Fixed a memory leak where message event listeners were not cleaned up after the popup or window closed

Checklist

• Version bumped