sway: replace swaylock with gtklock, Star Wars theme lockscreen

Switch lockscreen from swaylock to gtklock. CSS styled with Star Wars
yellow (#FFE81F) on near-black background, cover-scaled wallpaper injected
at runtime via temp CSS to avoid path expansion issues in gtklock config.
Update sway background wallpaper to darth-vader-sam.jpg.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ansible/inventory/group_vars/void.yml

@@ -160,6 +160,7 @@ desktop_sway_packages:
   - flameshot
   - foot
   - foot-terminfo
+  - gtklock
   - grim
   - kanshi
   - rofi
@@ -167,7 +168,6 @@ desktop_sway_packages:
   - swayfx
   - swaybg
   - swayidle
-  - swaylock
   - SwayOSD
   - Waybar
   - wl-clipboard