Feat/skeleton loading

[Sumanth2377]

Description

This PR implements skeleton loading for message images and workspace avatars, unifying the loading experience with the rest of the app.

Closes #4810

Changes

• Created a reusable Skeleton component in app/containers/Skeleton.
• Replaced OverlayComponent loading spinner with Skeleton in MessageImage.
• Added Skeleton loading to Markdown images.
• Added Skeleton loading to ServerAvatar in WorkspaceView.
• Removed unused dependencies: react-native-image-progress and react-native-progress.

Verification

• Verified skeleton appears while images are loading in messages.
• Verified skeleton appears on workspace avatars.
• Verified unit tests pass.

Summary by CodeRabbit

• New Features

  • New Emoji component with unified handling for standard and custom emoji
  • New Skeleton component for loading placeholders

• Improvements

  • Emoji rendering consolidated into the shared Emoji component across the app
  • Image and avatar flows now show skeleton placeholders while loading for smoother UX

• Tests

  • Unit tests added for Emoji and Skeleton components

• Chores

  • Public re-exports added for Emoji and Skeleton components

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