Replace phx-click server event with Fluxon.open_dialog for zero-latency
modal opening. The modal DOM is now always present (no :if conditional) so
it can be shown instantly; the server syncs state in the background.
Fix test selectors that now match the always-present modal form by scoping
to forms without phx-target (which the modal form always has).
Claudio Ortolina
621b35d824