Profiles: named layouts that open apps

A profile is a named layout plus the screens it hides and its apps' windows
(docs/profiles.md). ft-layout save captures them (ft-floatd's "windows",
after the KWin script reports every window as it is now); use opens them:
the screens move, open windows of each app go to their places (on a screen,
maximized or not, or floating), and missing apps start, once and then again
for each window still missing 3 s after the first. Nothing closes.

The desktop starts in FT_PROFILE or default_profile (ft-layout start, from
the session script). Each profile gets a launcher entry (Frametop: NAME, in
SteamVR's Launch a program list) that switches to it or starts the desktop
in it. The relay's profile:NAME action and Input Settings' "Open profile"
entries put one on a key, mouse button, or controller button. Display
Settings' Layout page becomes Layout & profiles: Save as profile, Open
profile, the profile's apps, and Start in profile. Plasma's own session
restore is off in the Frametop session.

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

docs/reference.md

@@ -139,8 +139,10 @@ Frametop Display Settings has four tabs (three with the gamescope backend, which
 ```
 layout/ft-layout apply      # arrange every screen
 layout/ft-layout capture    # save the current arrangement and sizes as the layout
-layout/ft-layout save NAME  # ...under a name too, and use it
-layout/ft-layout use NAME   # switch to a named layout and arrange the screens in it
+layout/ft-layout save NAME  # ...under a name too, with the open apps and hidden screens (a profile, docs/profiles.md), and use it
+layout/ft-layout use NAME   # switch to a profile: arrange the screens in it and open its apps
+layout/ft-layout open NAME  # a profile's launcher entry: use it, or start the desktop in it
+layout/ft-layout default NAME|none  # the profile the desktop starts with (start --wait runs it at desktop start)
 layout/ft-layout layouts    # list the named layouts (* = in use); rename OLD NEW, delete NAME
 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)