Add loading skeletons to feed cards

[aleibovici]

Description

When the feed is loading, the UI currently shows a simple loading state. Replace this with skeleton placeholder cards that match the shape of real post cards for a smoother perceived loading experience.

Suggested approach

• Create a PostCardSkeleton component with animated pulse placeholders
• Use Tailwind's animate-pulse class on gray placeholder blocks
• Match the layout of the real post card (avatar circle, name bar, text lines, action buttons)
• Show 3-5 skeleton cards while data is loading

Files to look at

• src/components/ — existing post card and feed components
• Look at how TanStack Query loading states are handled in src/hooks/

Great way to learn the component structure and Tailwind animation utilities.