displays: add "show on last display" for some components.

- Lets the components migrate when un-docked to the otehr monitor,
  basically

Common/SettingsData.qml

@@ -259,6 +259,7 @@ Singleton {
     property string updaterTerminalAdditionalParams: ""
 
     property var screenPreferences: ({})
+    property var showOnLastDisplay: ({})
 
     signal forceDankBarLayoutRefresh
     signal forceDockLayoutRefresh
@@ -494,6 +495,7 @@ Singleton {
                 widgetBackgroundColor = settings.widgetBackgroundColor !== undefined ? settings.widgetBackgroundColor : "sch"
                 surfaceBase = settings.surfaceBase !== undefined ? settings.surfaceBase : "s"
                 screenPreferences = settings.screenPreferences !== undefined ? settings.screenPreferences : ({})
+                showOnLastDisplay = settings.showOnLastDisplay !== undefined ? settings.showOnLastDisplay : ({})
                 wallpaperFillMode = settings.wallpaperFillMode !== undefined ? settings.wallpaperFillMode : "Fill"
                 animationSpeed = settings.animationSpeed !== undefined ? settings.animationSpeed : SettingsData.AnimationSpeed.Short
                 customAnimationDuration = settings.customAnimationDuration !== undefined ? settings.customAnimationDuration : 500
@@ -677,6 +679,7 @@ Singleton {
                                                 "updaterCustomCommand": updaterCustomCommand,
                                                 "updaterTerminalAdditionalParams": updaterTerminalAdditionalParams,
                                                 "screenPreferences": screenPreferences,
+                                                "showOnLastDisplay": showOnLastDisplay,
                                                 "animationSpeed": animationSpeed,
                                                 "customAnimationDuration": customAnimationDuration,
                                                 "acMonitorTimeout": acMonitorTimeout,
@@ -743,7 +746,7 @@ Singleton {
             "customPowerActionLock", "customPowerActionLogout", "customPowerActionSuspend",
             "customPowerActionHibernate", "customPowerActionReboot", "customPowerActionPowerOff",
             "updaterUseCustomCommand", "updaterCustomCommand", "updaterTerminalAdditionalParams",
-            "screenPreferences", "animationSpeed", "customAnimationDuration", "acMonitorTimeout", "acLockTimeout",
+            "screenPreferences", "showOnLastDisplay", "animationSpeed", "customAnimationDuration", "acMonitorTimeout", "acLockTimeout",
             "acSuspendTimeout", "acHibernateTimeout", "batteryMonitorTimeout", "batteryLockTimeout",
             "batterySuspendTimeout", "batteryHibernateTimeout", "lockBeforeSuspend",
             "loginctlLockIntegration", "launchPrefix", "brightnessDevicePins", "configVersion"
@@ -943,7 +946,11 @@ Singleton {
         if (prefs.includes("all")) {
             return Quickshell.screens
         }
-        return Quickshell.screens.filter(screen => prefs.includes(screen.name))
+        var filtered = Quickshell.screens.filter(screen => prefs.includes(screen.name))
+        if (filtered.length === 0 && showOnLastDisplay && showOnLastDisplay[componentId] && Quickshell.screens.length === 1) {
+            return Quickshell.screens
+        }
+        return filtered
     }
 
     function sendTestNotifications() {
@@ -1812,6 +1819,11 @@ Singleton {
         saveSettings()
     }
 
+    function setShowOnLastDisplay(prefs) {
+        showOnLastDisplay = prefs
+        saveSettings()
+    }
+
     function setBrightnessDevicePins(pins) {
         brightnessDevicePins = pins
         saveSettings()

Modules/Settings/DisplaysTab.qml

@@ -56,10 +56,21 @@ Item {
     }
 
     function setScreenPreferences(componentId, screenNames) {
-        var prefs = SettingsData.screenPreferences || {
+        var prefs = SettingsData.screenPreferences || {};
-        };
+        var newPrefs = Object.assign({}, prefs);
-        prefs[componentId] = screenNames;
+        newPrefs[componentId] = screenNames;
-        SettingsData.setScreenPreferences(prefs);
+        SettingsData.setScreenPreferences(newPrefs);
+    }
+
+    function getShowOnLastDisplay(componentId) {
+        return SettingsData.showOnLastDisplay && SettingsData.showOnLastDisplay[componentId] || false;
+    }
+
+    function setShowOnLastDisplay(componentId, enabled) {
+        var prefs = SettingsData.showOnLastDisplay || {};
+        var newPrefs = Object.assign({}, prefs);
+        newPrefs[componentId] = enabled;
+        SettingsData.setShowOnLastDisplay(newPrefs);
     }
 
     DankFlickable {
@@ -660,7 +671,6 @@ Item {
 
                                 Column {
                                     property string componentId: modelData.id
-                                    property var selectedScreens: displaysTab.getScreenPreferences(componentId)
 
                                     width: parent.width
                                     spacing: Theme.spacingXS
@@ -669,7 +679,7 @@ Item {
                                         width: parent.width
                                         text: I18n.tr("All displays")
                                         description: I18n.tr("Show on all connected displays")
-                                        checked: parent.selectedScreens.includes("all")
+                                        checked: displaysTab.getScreenPreferences(parent.componentId).includes("all")
                                         onToggled: (checked) => {
                                             if (checked)
                                                 displaysTab.setScreenPreferences(parent.componentId, ["all"]);
@@ -678,18 +688,29 @@ Item {
                                         }
                                     }
 
+                                    DankToggle {
+                                        width: parent.width
+                                        text: I18n.tr("Show on Last Display")
+                                        description: I18n.tr("Always show when there's only one connected display")
+                                        checked: displaysTab.getShowOnLastDisplay(parent.componentId)
+                                        visible: !displaysTab.getScreenPreferences(parent.componentId).includes("all") && ["dankBar", "dock", "notifications", "osd", "toast"].includes(parent.componentId)
+                                        onToggled: (checked) => {
+                                            displaysTab.setShowOnLastDisplay(parent.componentId, checked);
+                                        }
+                                    }
+
                                     Rectangle {
                                         width: parent.width
                                         height: 1
                                         color: Theme.outline
                                         opacity: 0.2
-                                        visible: !parent.selectedScreens.includes("all")
+                                        visible: !displaysTab.getScreenPreferences(parent.componentId).includes("all")
                                     }
 
                                     Column {
                                         width: parent.width
                                         spacing: Theme.spacingXS
-                                        visible: !parent.selectedScreens.includes("all")
+                                        visible: !displaysTab.getScreenPreferences(parent.componentId).includes("all")
 
                                         Repeater {
                                             model: Quickshell.screens