ui(mfa): dont require button click to validate mfa, do automatically

[wssheldon]

What does this PR do?

Remove button you have to click on/mfa to complete the flow.

Clicking the button to validate MFA is unnecessary, being able to navigate to the page is enough.

How did you verify your code works?

I wrote component level tests.

 ✓ src/tests/Mfa.spec.js (6)
   ✓ mounts correctly and starts verification automatically
   ✓ shows loading state while verifying
   ✓ shows success message and closes window on approval
   ✓ shows error message and retry button on denial
   ✓ retry button triggers new verification attempt
   ✓ handles API errors gracefully

 Test Files  1 passed (1)
      Tests  6 passed (6)
   Start at  09:11:58
   Duration  391ms

I manually test the new flow, end to end.

[kevgliss]

lgtm, aligns with how stairmaster does it as well.