The login form used 'return doLogin(event)' in onsubmit, but doLogin is
async so it returns a Promise (truthy), which some browsers interpret as
'proceed with native form submit'. Changed to 'doLogin(event);return false'
and added an explicit onkeydown Enter handler on the password input as
belt-and-suspenders.
Closes#124
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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