* feat: Add FIDO2/U2F security key support for lock screen
Adds hardware security key authentication (e.g. YubiKey) with two modes:
Alternative (OR) and Second Factor (AND). Includes settings UI, PAM
integration, availability detection, and proper state cleanup.
Also fixes persist:false properties being reset on settings file reload.
* feat: Add U2F pending timeout and Escape to cancel
Cancel U2F second factor after 30s or on Escape key press,
returning to password/fingerprint input.
* fix: U2F detection honors custom PAM override for non-default key paths
