fix: restore lock screen U2F/fingerprint auth to working state

[xPathin]

Summary

• Reverts breaking changes to Pam.qml introduced between 185284d4 and e86227f0 that broke FIDO2/U2F security key support on the lock screen
• Restores Process-based availability detection for fingerprint and U2F
• Restores correct PAM config fallback (removes /etc/pam.d/login watcher that overrides bundled U2F config)
• Restores proper U2F message handling (message.toLowerCase().includes("touch") instead of message !== "")

Fixes #2050

Test plan

• Enable U2F in Settings > Lock Screen
• Test OR mode: lock screen, verify YubiKey activates and "Insert/Touch your security key" prompts appear
• Test AND mode: lock screen, authenticate with password, verify YubiKey second factor prompt appears
• Test fingerprint auth still works if enrolled

[Purian23]

Hi there, thanks for looking into it. We'll do the same on our end as the changes that fixed yours previously, broke others which led to what we hoped would be general updates to work for everyone.

[Purian23]

Hey @xPathin give the updated commit a try. Some of the settings you reverted are not on the Stable branch of DMS v1.4.4, but are in the Master branch. We have a brand New Greeter UI for settings that I want to keep in sync with the LockScreen. Otherwise I think what you updated along with the changes in place should resolve both issues.

[xPathin]

Hey @xPathin give the updated commit a try. Some of the settings you reverted are not on the Stable branch of DMS v1.4.4, but are in the Master branch. We have a brand New Greeter UI for settings that I want to keep in sync with the LockScreen. Otherwise I think what you updated along with the changes in place should resolve both issues.

Thank you, all working for me!
LGTM