Launch apps in their own scope instead of the compositor's cgroup (#6541)

* Launch apps in their own scope instead of the compositor's cgroup

The launcher ran desktop entries through gtk-launch, so the app inherited
quickshell's cgroup, which belongs to wayland-wm@hyprland.desktop.service.
A kernel OOM kill there fails the compositor unit and tears down the whole
session, dropping the user at SDDM with every window lost. A single runaway
app took the desktop down three times in one afternoon.

Route launches through uwsm-app so each app gets its own scope under
app-graphical.slice. A runaway app now fails its own scope and the session
keeps running.

The post-install launches had the same inheritance bug in a milder form,
where the app landed in the installer terminal's scope and died with it.
0aedef58 patched that with setsid, which detaches the session but leaves
cgroup membership behind. A scope fixes it properly.

* Detach post-install app launches

* Preserve desktop entry launch compatibility

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Co-authored-by: David Heinemeier Hansson <david@hey.com>

bin/omarchy-install-editor-emacs

@@ -6,4 +6,4 @@ echo "Installing Emacs..."
 omarchy-pkg-aur-add omarchy-emacs && omarchy-install-emacs
 
 # emacsclient opens a frame on the running daemon, not a second Emacs
-setsid gtk-launch emacsclient
+setsid uwsm-app -- gtk-launch emacsclient >/dev/null 2>&1 &