use:enhance vs callback form variant rendering, self-relation
error, submit disabled on missing related person, submit disabled
on yearError.
5 new tests covering ~10 branches.
Refs #496.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Toggle button, form open on click, all relationship type options,
year-error alert when toYear < fromYear, no-error path when equal,
cancel button closes form, onSubmit prop wiring.
7 tests covering ~20 branches.
Refs #496.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
