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>

docs/reference.md

@@ -48,7 +48,7 @@ The Visibility & pins tab of Frametop Display Settings decides when the screens
 - While you look at a chosen controller (the wrist gesture).
 - Only after you show them with the hotkey.
 
-In the last three modes the hotkey shows the screens anyway. Two more settings on the same tab cover VR games, which ft-screens detects as SteamVR scene apps:
+In the last three modes the hotkey shows the screens anyway. A screen can also be hidden on its own (Screens shown on the same tab, or `ft-layout hide N`): it stays hidden whatever the mode or the hotkey says, until it's shown again there. Windows on it stay put, and a new window that would open on it floats instead (ft-floatd). Profiles use this to show only some screens. Two more settings on the same tab cover VR games, which ft-screens detects as SteamVR scene apps:
 
 - During VR games, the Always mode hides the screens unless the dashboard is open (the default), or leaves them up.
 - Controllers on the screens. Visible screens can keep SteamVR's laser mouse on, so controllers work them with the dashboard closed, but that also takes the controllers away from a game. By default this is off while a VR game runs, and the 3D mouse or the dashboard works the screens. The other choices are always on, or only with the dashboard open, which also suits flatscreen games since they aren't scene apps.
@@ -146,6 +146,7 @@ layout/ft-layout pin N|all left|right|head   # pin as they are now; unpin N|all
 layout/ft-layout plan       # print the arrangement as JSON (no VR needed)
 layout/ft-layout scale      # per-screen scale, positions (as the screens are around you), and taskbar screen, to KWin
 layout/ft-layout toggle     # hide or show all screens
+layout/ft-layout hide N|all # hide a screen on its own, whatever the visibility mode; show N|all brings it back, hidden lists them
 display-settings/install.sh # menu entries and the Meta+Shift+R and Meta+Shift+H shortcuts
 ```