Implement --detach for panel kitten

docs/kittens/panel.rst

@@ -80,7 +80,7 @@ disappears at a key press. To do so use the following command::
     kitty +kitten panel --edge=top --layer=overlay --lines=15 \
         --focus-policy=exclusive --exclusive-zone=0 --override-exclusive-zone \
         -o background_opacity=0.8 --toggle-visibility --single-instance \
-        --instance-group=quake
+        --instance-group=quake --detach
 
 Run this command in a terminal, and a quick access kitty panel will show up at
 the top of your screen. Run it again, and the panel will be hidden.

kittens/panel/main.py

@@ -183,6 +183,11 @@ type=bool-set
 Start in hidden mode, useful with :option:`--toggle-visibility`.
 
 
+--detach
+type=bool-set
+Detach from the controlling terminal, if any.
+
+
 --debug-rendering
 type=bool-set
 For internal debugging use.
@@ -338,6 +343,9 @@ def handle_single_instance_command(boss: BossType, sys_args: Sequence[str], envi
 def main(sys_args: list[str]) -> None:
     global args
     args, items = parse_panel_args(sys_args[1:])
+    if args.detach:
+        from kitty.utils import detach
+        detach()
     sys.argv = ['kitty']
     if args.debug_rendering:
         sys.argv.append('--debug-rendering')