Use [key: string]: unknown index signature so TS does not reject the
extra fields (location, status) passed to the redirect/failure result
in the spec helpers.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Use createUnsavedWarning() + UnsavedWarningBanner to replace the inline
beforeNavigate/isDirty pattern, and add an enhance callback that calls
clearOnSuccess() before update() so the guard is disarmed before
SvelteKit's internal goto() fires on a redirect result.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>