desktop: add sway/swayfx profile (dormant) with waybar, kanshi, cliphist

New profile_desktop_sway role gated by desktop_sessions_enabled, with
SwayFX effects, Waybar bar (1:1 with Polybar layout + pulseaudio),
swayidle + swaylock-effects for locking, swayosd for OSD, cliphist for
clipboard history and kanshi for multi-monitor profiles. Emptty gains
WAYLAND_SESSIONS_PATH + wayland-sessions dir. start-sway wrapper handles
session env (dbus-run-session, gpg-agent, turnstile env). Profile stays
dormant until a host opts in via desktop_sessions_enabled.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

dotfiles/desktop/.local/bin/start-sway

@@ -0,0 +1,24 @@
+#!/bin/sh
+
+[ -r /etc/profile ]    && . /etc/profile
+[ -r "$HOME/.profile" ] && . "$HOME/.profile"
+
+export XDG_CURRENT_DESKTOP=sway
+export XDG_SESSION_DESKTOP=sway
+export XDG_SESSION_TYPE=wayland
+
+export MOZ_ENABLE_WAYLAND=1
+export QT_QPA_PLATFORM='wayland;xcb'
+export _JAVA_AWT_WM_NONREPARENTING=1
+export SDL_VIDEODRIVER=wayland
+export GDK_BACKEND='wayland,x11'
+
+export SSH_AUTH_SOCK="$HOME/.local/state/ssh-agent/socket"
+
+exec dbus-run-session sh -eu -c '
+  umask 077
+  printf "%s\n" "$DBUS_SESSION_BUS_ADDRESS" > "$HOME/.dbus-session-bus-address"
+  gpgconf --launch gpg-agent
+  "$HOME/.local/bin/update-turnstile-env"
+  exec sway
+'