Add mobile-responsive layout for the upload page

[eshankiyer]

The upload page had no responsive breakpoints, so on a phone the pipeline row (the model selects, the connector arrows, and the Run button) gets squeezed onto one horizontal line and the card padding eats most of the screen.

This adds a single @media (max-width: 768px) block to UploadPage.css that:

• stacks the pipeline row vertically and rotates the connector arrows to point down
• • makes the Run button full-width with a larger tap target
• • tightens the page, card, and dropzone padding and trims the CT preview height
    The rules only apply at 768px and below, so desktop is unchanged. CSS only, no markup or JS changes.