Replace dunst with swaync for fractional scaling support

Dunst lacks wp_fractional_scale_v1, causing jagged font rendering
on external monitors in mixed-DPI setups (laptop 2.5x + externals 1x).
swaync (GTK4) handles fractional scaling natively.

Style based on catppuccin/swaync with Lavender accent.

defaults/xdg/niri/config.kdl

@@ -79,7 +79,7 @@ layout {
 // xwayland-satellite is managed automatically since niri 25.08
 // kanshi is managed via systemd user service (kanshi.service)
 spawn-at-startup "waybar"
-spawn-at-startup "dunst" "-conf" "/etc/xdg/dunst/dunstrc"
+spawn-at-startup "swaync"
 spawn-at-startup "/usr/lib/polkit-gnome/polkit-gnome-authentication-agent-1"
 spawn-at-startup "nm-applet" "--indicator"
 spawn-sh-at-startup "waypaper --restore"
@@ -134,7 +134,7 @@ binds {
 
     Mod+Return hotkey-overlay-title="Open a Terminal: foot" { spawn "foot"; }
     Mod+Space hotkey-overlay-title="Run an Application: walker" { spawn "walker"; }
-    Super+Alt+L hotkey-overlay-title="Session Menu: moonset" { spawn "moonset"; }
+    Mod+Escape hotkey-overlay-title="Session Menu: moonset" { spawn "moonset"; }
 
     Mod+A { spawn "walker" "-s" "audio"; }
 
@@ -272,7 +272,7 @@ binds {
     Ctrl+Print { screenshot-screen; }
     Alt+Print { screenshot-window; }
 
-    Mod+Escape allow-inhibiting=false { toggle-keyboard-shortcuts-inhibit; }
+    Super+Alt+L allow-inhibiting=false { toggle-keyboard-shortcuts-inhibit; }
 
     Mod+Shift+E { quit; }
     Ctrl+Alt+Delete { quit; }