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>

dotfiles/desktop/.config/sway/config

@@ -62,6 +62,11 @@ gaps outer 4
 smart_gaps on
 smart_borders on
 
+# Window rules
+for_window [app_id="(?i)polkit"] floating enable
+for_window [class="(?i)polkit"] floating enable
+for_window [title="^Authentication Required"] floating enable
+
 # Autostart — XDG and session services
 exec dex --autostart --environment sway
 exec gnome-keyring-daemon --start --components=secrets
@@ -85,6 +90,7 @@ exec /usr/libexec/xfce-polkit
 exec nm-applet
 exec blueman-applet
 exec udiskie
+exec flameshot
 
 # Clipboard manager (Wayland-native)
 exec wl-paste --type text  --watch cliphist store
@@ -125,10 +131,13 @@ bindsym $mod+Shift+x exec ~/.config/sway/scripts/lockscreen
 # Kill focused window
 bindsym $mod+Shift+q kill
 
-# Screenshot (xfce4-screenshooter via xdg-desktop-portal-wlr)
-bindsym Print exec xfce4-screenshooter
-bindsym Shift+Print exec xfce4-screenshooter -r
-bindsym Alt+Print exec xfce4-screenshooter -w
+# Screenshot
+#   Print        → flameshot GUI (annotations, save + clipboard via portal)
+#   Shift+Print  → grim+slurp region → clipboard
+#   Alt+Print    → grim focused output → clipboard
+bindsym Print exec flameshot gui --path "$HOME/Pictures/Screenshots" --clipboard
+bindsym Shift+Print exec ~/.config/sway/scripts/screenshot region
+bindsym Alt+Print exec ~/.config/sway/scripts/screenshot output
 
 # Focus
 bindsym $mod+$left focus left