[Enhancement] Add progress steps indicator (Upload → Configure → Export → Download)

[magic-peach]

Overview

Add a visual progress stepper at the top of the page showing the user where they are in the workflow: Upload → Configure → Export → Download.

Design

● Upload → ○ Configure → ○ Export → ○ Download

Each step activates when reached.

Implementation

Map steps to status values:

• Upload: file is null
• Configure: file is set, status is idle
• Export: status is loading-engine or exporting
• Download: status is done

Acceptance Criteria

• 4-step indicator visible at top of page
• Active step highlighted
• Completed steps show checkmark
• Accessible with ARIA

[kunal-yelgate]

Hi @magic-peach👋

I would like to work on this issue (#98).
I have experience with frontend/UI improvements and open-source contributions, and I’m confident I can provide a clean and efficient solution.

Please assign this issue to me. Looking forward to contributing to the project.

[magic-peach]

@kunal-yelgate please star the repo