Improve portability and add lid close setup

- Replace hardcoded sleep hook with swayidle in niri autostart
- Replace hardcoded dotfiles path in powermenu bind with plain 'powermenu'
- Replace hardcoded wofi style path with XDG path (~/.config/wofi/style.css)
- Update install.sh to symlink powermenu to ~/.local/bin and wofi/style.css
- Switch display manager from GDM to greetd with tuigreet
- Add logind drop-in for lid close: suspend on battery, lock on AC

niri/config.kdl

@@ -17,6 +17,7 @@ spawn-at-startup "mako"
 spawn-at-startup "swww-daemon"
 spawn-at-startup "nm-applet" "--indicator"
 spawn-at-startup "polkit-gnome-authentication-agent-1"
+spawn-at-startup "swayidle" "-w" "before-sleep" "swaylock -f -c 000000"
 
 binds {
     Mod+Q repeat=false { close-window; }
@@ -39,7 +40,7 @@ binds {
     Print { spawn-sh "grim -g \"$(slurp)\" ~/Pictures/screenshot-$(date +%s).png"; }
 
     Mod+Shift+E { spawn "swaylock" "-f" "-c" "000000"; }
-    Mod+Shift+P { spawn "bash" "/home/alex/Documents/dotfiles/scripts/powermenu.sh"; }
+    Mod+Shift+P { spawn "powermenu"; }
     Mod+Shift+X { quit; }
 
     XF86AudioRaiseVolume allow-when-locked=true { spawn "pamixer" "-i" "5"; }