Establishes the pattern the remaining 15 add/edit forms will follow:
- The form component accepts open?/id? props. When open is defined it's
used as-is; asModal is fixed at mount (not reactive) since the parent
decides once whether this instance is a modal or a route page.
- As a modal it renders through BaseFormModal (header=title, footer=
buttons, body=form) and emits success + update:open instead of
navigating; as a route page (the old /city/create still exists and still
works) it falls back to the original <a-card> + button layout unchanged.
- The list page gets a ListPageHeader add button above the list, gated on
the exact rid the route used to gate on (cities.create), opening the
modal instead of navigating.
Verified: pnpm build passes.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
