Fix the installer; start the desktop without the Steam client's environment

install.sh: a comment with an apostrophe inside a single-quoted command
(from the distrobox pin) ended the quote and broke the script at step 1.

The VR launcher started the desktop with the Steam client's environment,
including LD_LIBRARY_PATH to Steam's runtime, whose libavcodec has no
H.264 decoder: VLC in the desktop couldn't play most videos. The session
script now drops the client's variables before starting anything, so apps
use the system's libraries and codecs.

The README and the installer now recommend setting Steam's Sleep after
(When Plugged In and Idle) to Never; Steam suspends the Frame after an
hour otherwise, even while charging.

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

session/frametop-session.sh

@@ -16,6 +16,19 @@
 set -eu
 
 here=$(dirname "$(readlink -f "$0")")
+
+# Started from the VR launcher, the desktop inherits the Steam client's environment. Apps in
+# it should see the system as a normal login does, so drop the client's runtime: its
+# LD_LIBRARY_PATH put Steam's own libraries ahead of the system's (Steam's libavcodec has no
+# H.264 decoder, so VLC couldn't play most videos), and its overlay and launch settings are
+# meant for games. SteamOS's own defaults (/usr/share/deckard/mesavars.sh) stay.
+for var in $(compgen -e); do
+  case $var in
+    LD_LIBRARY_PATH | LD_PRELOAD | STEAM_* | Steam* | SRT_* | PRESSURE_VESSEL_* | MANGOHUD_* | \
+      ENABLE_VK_LAYER_VALVE_steam_overlay_* | STEAMVIDEOTOKEN) unset "$var" ;;
+  esac
+done
+
 conf=$HOME/.config/frametop.conf
 BACKEND=screens SCREENS=2 WIDTH=1920 HEIGHT=1080 PHYS_WIDTH=1.6 REMOTE=0
 # shellcheck disable=SC1090
@@ -46,7 +59,6 @@ if [ "${1:-}" != --inner ]; then
   # Plasma can't find them and opens Discover instead.
   export XDG_DATA_DIRS=${XDG_DATA_DIRS:-/usr/local/share:/usr/share}
   set +u; . /etc/profile.d/flatpak.sh; set -u
-  unset LD_PRELOAD
   # Arrange the screens in the saved layout once they're up (layout; skipped
   # when auto-arrange is off).
   setsid "$here/../layout/ft-layout" apply --wait 90 > /tmp/frametop-layout.log 2>&1 < /dev/null &
@@ -80,8 +92,11 @@ if [ "${1:-}" != --inner ]; then
   exit
 fi
 
-# Inside the host compositor (ft-screens or gamescope) from here on.
-unset LD_PRELOAD XDG_DESKTOP_PORTAL_DIR
+# Inside the host compositor (ft-screens or gamescope) from here on. The desktop isn't a
+# gamescope client with ft-screens, so the gamescope session's Vulkan layer stays off, and
+# the gamescope session's portal config isn't Plasma's.
+[ "$backend" = gamescope ] || unset ENABLE_GAMESCOPE_WSI
+unset XDG_DESKTOP_PORTAL_DIR
 [ "$backend" = gamescope ] || screens=${FT_SCREEN_COUNT:-$screens}
 
 host_runtime=$XDG_RUNTIME_DIR