Add an eye/eye-off button inside the password field so a typed password can
be checked against what was intended — the difference between "wrong
password" and "wrong keyboard" was previously invisible.
`bind:value` is not allowed alongside a dynamic `type`, so the field is wired
manually via value/oninput; unlike branching on two separate inputs, this
keeps focus and caret position when the toggle is pressed.
Both fields also get autocapitalize/autocorrect/spellcheck off and proper
autocomplete hints. The Android soft keyboard was free to capitalise or
autocorrect the username, which silently changes a credential the user
believes they typed correctly.