refactor: update README for clarity and structure; add demo GIF

[NoxelS]

Summary

Validation

• npm test
• npm run package:vsix when packaging or manifest behavior changed
• Manual VS Code validation when activation, commands, settings, or UI behavior changed

Checklist

• I kept this pull request focused.
• I updated tests and documentation where needed.
• I did not include credentials, user documents, or endpoint URLs containing sensitive data.
• I documented any change to data handling, privacy, or endpoint behavior.