The Add-account modal only ever generated a one-time password — there was no way to set
one. Add an optional password field (with a show/hide toggle):
- blank → previous behaviour: a strong one-time password is generated, the account is
flagged must_change_password, and the clear text is revealed once.
- filled → that becomes the user's own login (validated min 12 / mixed case / digit);
must_change_password stays false (no forced rotation) and nothing is revealed.
Browser-verified: the modal shows the password field + hint; both paths covered by tests.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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