Migrate all remaining `delete-button` usages to the `link-action` and
`show-modal` + `form-fetch-action` mechanisms and remove the
`initGlobalDeleteButton` handler, as its FIXME requested.
The new request shape required two backend tweaks: webauthn key delete
reads `id` from the query string, and account deletion returns
`JSONError` on validation failure so fetch-action can display it.
Assisted-by: claude-code:opus-4.8
b74c3a9f6c