fix: keep keyboard focus on the credential field

Bind each field's focus to the stage so the greeter's window
activation has a focus target and focus follows the stage switch.
The startup focusStage() ran while the view was still hidden, where
forceActiveFocus() is dropped, so re-ask once from a short one-shot
timer after the view is on screen.

Verified in sddm-greeter --test-mode: username focused at start,
password focused after advancing.

0 files changed, 0 insertions, 0 deletions