Salvage trim of #114291:
- Drop the separate `confirming` state: `setSelecting(backend.name)` now
wraps the whole select flow (confirm step included), so the existing
`selecting` guard and `disabled` binding already refuse a second click
while the dialog is open — no second state to keep in sync.
- Tests: keep the two invariants (confirm gates the persist; declining
never persists) and drop the double-click test, whose behaviour is now
the pre-existing selecting guard. Revert the unrelated edit to the
already-active-backend test.
014f395b74