Right-align the Change image button on the project About page

Problem

On the project About page, the Change image button sits next to the project image but isn't aligned with it, so it looks out of place.

Expected behavior

Move the Change image button to the trailing (right) edge of its section instead of placing it beside the image.

Acceptance criteria

• The button is right-aligned in the About header or section and vertically aligned with the image in a consistent way (e.g. centered on it).
• The button is still shown only to viewers with write access (TRACK-19).
• At narrow widths the button doesn't overlap the project name or description. It wraps cleanly if there isn't room.
• Works in light and dark modes, with focus and hover states unchanged.