accessibility: Keyboard navigation skips submit button — can't complete form without mouse

[sshdopey]

Problem

Tab through investment form fields, submit button is not in tab order.

[Fhatu12]

Hi, I'd like to work on this issue. I’ll keep the change focused on restoring keyboard access to the investment form submit control, add regression coverage for Tab/focus behaviour, and avoid unrelated form or wallet-flow changes. Please assign me before I proceed.