remove nm-applet and blueman-applet autostart

Both daemons were running but not registering SNI items on niri/Wayland,
leaving the waybar tray slot permanently empty. Network is already
accessible via the waybar network module (left-click → networkmanager_dmenu).
Bluetooth GUI (blueman-manager) is still available on demand; only the
applet is dropped.

Tray module stays configured so Electron apps (Discord/Vesktop, Steam,
etc.) still get a tray slot when they're running.

- niri/config.kdl: drop nm-applet and blueman-applet spawn-at-startup
- packages.txt: drop network-manager-applet (nothing else uses it);
  keep blueman package for blueman-manager GUI

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages.txt

@@ -14,7 +14,6 @@ gtklock
 swayidle
 snixembed
 ttf-jetbrains-mono-nerd
-network-manager-applet
 polkit-gnome
 xdg-desktop-portal-wlr
 thunar