chore: misc tweaks — nm-applet autostart, thunar, SUPER+Q close, monitor preset

- autostart nm-applet --indicator under uwsm-app
- install networkmanagerapplet system-wide
- swap Nautilus for Thunar in file-manager bindings
- close-window bound to SUPER+Q (was SUPER+W)
- switch the active monitor preset from retina/2x to 1x 1080p/1440p
- summer-night waybar: drop custom/battery + backlight from modules-right

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

core/system/network.nix

@@ -25,4 +25,8 @@ in
       DNSOverTLS=opportunistic
     '';
   };
+
+  environment.systemPackages = [
+   pkgs.networkmanagerapplet
+  ];
 }