feat(driver): add TapSelector and make mock WaitForIdle honor duration

Real maestro driver will resolve selectors itself rather than
forcing the runner to look up coordinates from the hierarchy. Mock
now waits the requested duration so tests don't busy-spin and
starve the SDK fixture goroutine.

internal/driver/driver.go

@@ -13,6 +13,7 @@ type Driver interface {
 	Terminate(ctx context.Context) error
 
 	Tap(ctx context.Context, x, y int) error
+	TapSelector(ctx context.Context, selector string) error
 	InputText(ctx context.Context, text string) error
 
 	Hierarchy(ctx context.Context) (string, error)