Session: don't autostart Discover's notifier or IBus in the desktop

The nested Plasma session runs the system's XDG autostart entries. Discover's update
notifier (/etc/xdg/autostart/org.kde.discover.notifier.desktop) started
plasma-discover --mode update inside it, 520-620 MB resident and about 9% of a core,
with flatpak-system-helper and AppStream downloads behind it. IBus started a nested
ibus-daemon with kimpanel and ibus-extension-gtk3, which no app in the desktop can use:
KWin's input method is ft-textinput (zwp_input_method_v1, focus reports only; the VR
keyboard types through ft-screens' seat), and the session already drops QT_IM_MODULE,
GTK_IM_MODULE and XMODIFIERS. Nothing in Frametop talks to IBus.

Before Plasma starts, the session script copies both entries into
$XDG_CONFIG_HOME/autostart with Hidden=true, which plasma-session honours for that
desktop only. It does this once ([Defaults] autostart=1 in frametoprc) and skips a name
the user already has a file for, so deleting the copy brings the program back. The
geoclue demo agent stays (it answers apps' location requests outside GNOME and idles at
0%), and orca's entry is OnlyShowIn GNOME-family desktops, so it never ran. Tested
against a temporary XDG_CONFIG_HOME, including an existing user ibus.desktop left alone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/reference.md

@@ -26,6 +26,8 @@ kwriteconfig6 --file ~/.config/frametop/kwinrc --group Plugins --key contrastEna
 kwriteconfig6 --file ~/.config/frametop/kdeglobals --group KDE --key AnimationDurationFactor 1
 ```
 
+Two of the system's autostart programs don't start in this desktop: Discover's update notifier (`org.kde.discover.notifier`), which starts Discover to check for updates, and IBus (`ibus`), which can't reach the desktop's apps because KWin's input method is `input/ft-textinput`. The session script puts copies with `Hidden=true` in `~/.config/frametop/autostart` once (marked in `frametoprc`), and skips a name you already have a file for. Delete a copy to start that program again.
+
 Settings are in two files, and Frametop Display Settings edits both. The screens (resolution, width in metres, scale, curve, which one has the taskbar) and their layout are in `~/.config/frametop-layout.json`. The backend, remote desktop, and pointer settings are in `~/.config/frametop.conf`; `session/frametop.conf.example` lists every key.
 
 Restarting the desktop closes its windows. Before the unit stops, `session/keep-apps.sh` moves every program started in the desktop into a systemd scope of its own, so background work such as servers, tmux, and builds keeps running. An app that shuts down its own helper processes when its window closes will still lose them; run that kind of work outside the desktop, for example as a systemd user service.