sway: center wallpaper, fix lockscreen flags and add idle timeouts

- Use bg mode 'center' so the wallpaper keeps its native size.
- Drop --clock and --indicator from the lockscreen invocation; those
  flags belong to swaylock-effects and made vanilla swaylock exit with
  an unknown-option error. Keep --indicator-idle-visible to preserve
  the ring while idle.
- Replace the suspend-only swayidle line with a full idle policy:
  5 min lock, 10 min DPMS off, DPMS on on resume, lock before sleep.

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

dotfiles/desktop/.config/sway/config

@@ -32,7 +32,7 @@ input * {
 seat * xcursor_theme Yaru 24
 
 # Outputs
-output * bg ~/.config/sway/wallpapers/wallpaper-161664.jpg fill
+output * bg ~/.config/sway/wallpapers/wallpaper-161664.jpg center
 
 # SwayFX effects
 corner_radius 8
@@ -90,8 +90,16 @@ exec udiskie
 exec wl-paste --type text  --watch cliphist store
 exec wl-paste --type image --watch cliphist store
 
-# Lock on suspend
-exec swayidle -w before-sleep '~/.config/sway/scripts/lockscreen'
+# Idle / lock policy
+#   5 min  idle  → lock
+#   10 min idle  → screen off (DPMS)
+#   resume       → screen on
+#   before sleep → lock
+exec swayidle -w \
+    timeout 300 '~/.config/sway/scripts/lockscreen' \
+    timeout 600 'swaymsg "output * dpms off"' \
+        resume 'swaymsg "output * dpms on"' \
+    before-sleep '~/.config/sway/scripts/lockscreen'
 
 # Terminal
 bindsym $mod+Return exec alacritty