Adds a small top-centered <Toast> that fires only when the Server
Action returns { ok: true } (i.e., the DB write actually succeeded).
Auto-dismisses after 3s.
Wires both create dialogs (CreateAccountDialog, CreateUserDialog) with
an onSuccess callback that the table parent uses to push the toast,
and the delete confirm-flow does the same. Inline-edit success stays
quiet (no toast) — only add/delete trigger it, per the requested
scope.
