feat: Add FIDO2/U2F security key support for lock screen (#1842)

* 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

quickshell/Common/settings/Processes.qml

@@ -18,6 +18,10 @@ Singleton {
         fprintdDetectionProcess.running = true;
     }
 
+    function detectU2f() {
+        u2fDetectionProcess.running = true;
+    }
+
     function checkPluginSettings() {
         pluginSettingsCheckProcess.running = true;
     }
@@ -57,6 +61,16 @@ Singleton {
         }
     }
 
+    property var u2fDetectionProcess: Process {
+        command: ["sh", "-c", "(test -f /usr/lib/security/pam_u2f.so || test -f /usr/lib64/security/pam_u2f.so) && (test -f /etc/pam.d/dankshell-u2f || test -f \"$HOME/.config/Yubico/u2f_keys\")"]
+        running: false
+        onExited: function (exitCode) {
+            if (!settingsRoot)
+                return;
+            settingsRoot.u2fAvailable = (exitCode === 0);
+        }
+    }
+
     property var pluginSettingsCheckProcess: Process {
         command: ["test", "-f", settingsRoot?.pluginSettingsPath || ""]
         running: false

quickshell/Common/settings/SettingsSpec.js

@@ -317,6 +317,9 @@ var SPEC = {
     enableFprint: { def: false },
     maxFprintTries: { def: 15 },
     fprintdAvailable: { def: false, persist: false },
+    enableU2f: { def: false },
+    u2fMode: { def: "or" },
+    u2fAvailable: { def: false, persist: false },
     lockScreenActiveMonitor: { def: "all" },
     lockScreenInactiveColor: { def: "#000000" },
     lockScreenNotificationMode: { def: 0 },

quickshell/Common/settings/SettingsStore.js

@@ -9,6 +9,9 @@ function parse(root, jsonObj) {
 
     for (var k in SPEC) {
         if (k === "pluginSettings") continue;
+        // Runtime-only keys are never in the JSON; resetting them here
+        // would wipe values set by detection processes on every reload.
+        if (SPEC[k].persist === false) continue;
         if (!(k in jsonObj)) {
             root[k] = SPEC[k].def;
         }