sway: screenshots, polkit floating, flatpak dark theme

Screenshots
- Swap xfce4-screenshooter for flameshot + grim/slurp/jq; xfce4 used
  the X11 selection so clipboard didn't round-trip to Wayland clients.
  Print invokes flameshot's editor; Shift/Alt+Print are quick
  grim-based captures via a small wrapper script. Flameshot is now
  autostarted so the first capture isn't slow.

Polkit
- Add for_window rules so the xfce-polkit dialog (and any other polkit
  agent) always opens floating.

Flatpak dark theme
- Write /etc/flatpak/overrides/global with GTK_THEME=Yaru-Blue-dark for
  legacy GTK apps, plus a sway-portals.conf so the Settings portal is
  served by xdg-desktop-portal-gtk (wlr doesn't implement it). That
  lets libadwaita apps see color-scheme=prefer-dark.

cleanup-sway: track the new package set.

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

ansible/inventory/group_vars/void.yml

@@ -174,8 +174,12 @@ desktop_i3_packages:
 desktop_sway_packages:
   - cliphist
   - dunst
+  - flameshot
+  - grim
+  - jq
   - kanshi
   - rofi
+  - slurp
   - swayfx
   - swaybg
   - swayidle
@@ -183,7 +187,6 @@ desktop_sway_packages:
   - SwayOSD
   - Waybar
   - wl-clipboard
-  - xfce4-screenshooter
   - xdg-desktop-portal-wlr
   - xorg-server-xwayland