settings: don't render a missing ack budget as "waits 0s"

An older sessiond has no lock_ack_budget_secs. Show the upgrade note instead of
inventing a number.

surfaces/quickshell/modules/settings/IdleConfig.qml

@@ -236,13 +236,27 @@ ContentPage {
             }
         }
 
+        // Only claim the ordering guarantee when the daemon actually reports
+        // the field. An older sessiond has no lock_ack_budget_secs, and
+        // rendering that absence as "waits 0s" would be the page inventing a
+        // number — the same class of lie as the timers this section replaced.
         StyledText {
             Layout.fillWidth: true
+            visible: SessiondPolicy.available && SessiondPolicy.lockAckBudgetSecs > 0
             wrapMode: Text.WordWrap
             color: Appearance.colors.colSubtext
             font.pixelSize: Appearance.font.pixelSize.smaller
             text: Translation.tr("The screen never goes dark on an unlocked session. sessiond locks first and waits %1s for the compositor to acknowledge; if it cannot, it blanks anyway and records a security error rather than pretending the session locked.")
                 .arg(SessiondPolicy.lockAckBudgetSecs)
         }
+
+        StyledText {
+            Layout.fillWidth: true
+            visible: SessiondPolicy.available && SessiondPolicy.lockAckBudgetSecs === 0
+            wrapMode: Text.WordWrap
+            color: Appearance.colors.colSubtext
+            font.pixelSize: Appearance.font.pixelSize.smaller
+            text: Translation.tr("This sessiond predates the lock-before-blank ordering. Update the souveraine package to get it.")
+        }
     }
 }