Hide screens one at a time

ft-screens: "conceal <screen|all>" hides a screen on its own, whatever the
visibility mode or the hotkey says, until "reveal"; "concealed" lists them.
(Not "hide N": older builds read anything starting with "hide" as the hotkey.)
ft-layout keeps it per screen ("hidden" in the layout), applies it when it
arranges the screens, and has hide/show N|all and hidden. Display Settings
gets a Shown switch per screen on the Visibility tab. ft-floatd floats a new
window that opens on a hidden screen, and puts a stray window on a screen
that shows. Profiles (next) use it to show only some screens.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

display-settings/main.qml

@@ -802,6 +802,27 @@ Kirigami.ApplicationWindow {
                         }
                     }
 
+                    Kirigami.Separator { Kirigami.FormData.isSection: true; Kirigami.FormData.label: "Screens shown" }
+
+                    Repeater {
+                        model: backend.screensShown
+                        delegate: Controls.Switch {
+                            required property var modelData
+                            required property int index
+                            Kirigami.FormData.label: "Screen " + (index + 1) + ":"
+                            text: modelData ? "Shown" : "Hidden"
+                            checked: modelData
+                            onToggled: backend.setScreenShown(index, checked)
+                        }
+                    }
+                    Controls.Label {
+                        text: "A hidden screen stays hidden whatever the choices above say, and Meta+Shift+H doesn't bring it back. Windows on it stay there; new ones that would open on it float instead."
+                        opacity: 0.7
+                        font: Kirigami.Theme.smallFont
+                        wrapMode: Text.Wrap
+                        Layout.maximumWidth: Kirigami.Units.gridUnit * 26
+                    }
+
                     Kirigami.Separator { Kirigami.FormData.isSection: true; Kirigami.FormData.label: "Pinned screens" }
 
                     Repeater {