Add screenshots to the getting-started tutorial

## Description

Add screenshots to the getting-started tutorial at key milestones to help new users orient themselves visually. This was deferred from the tutorial creation task to keep scope manageable.

## Suggested Screenshots

- Connection created and schema synced
- First node added to the graph view
- Expanded neighbors visible on the canvas
- Styled nodes (e.g., colored by property)
- Data table view

Keep the number of screenshots small (4-6) focused on major milestones rather than every click. This reduces maintenance burden when the UI changes.

## Dependencies

- #1716 (tutorial must be written first)

## Related Issues

- Part of #1097