Bug 2547768

**Summary:** opening the Input Method Selector auto-starts the KDE shutdown
service `org.kde.Shutdown`, which then stays resident and makes the desktop's
*Shut Down* entry stop working.

## Environment

- Fedora 44, KDE Plasma 6.7.5 on Wayland
- `im-chooser-1.7.6-1.fc44`, `im-chooser-common-1.7.6-1.fc44`

## Steps to reproduce

1. Log in to a Plasma 6 Wayland session.
2. Open the Input Method Selector (`im-chooser`) and close it again. No button
   has to be pressed, and no input method has to be changed.
3. Check the service that got activated at the same second:

   ```bash
   systemctl --user status 'dbus-:1.1-org.kde.Shutdown'
   ```

4. Click *Shut Down* in the KDE Application Launcher.

## Actual result

Step 2 silently starts `/usr/bin/plasma-shutdown`, which never exits, and step 4
then does nothing at all. The user journal shows:

```
10:23:11 systemd[1325]: Started app-im-chooser@....service - 输入法选择器.
10:23:11 systemd[1325]: Started dbus-:1.1-org.kde.Shutdown.
...
11:10:23 systemd[1325]: Started dbus-:1.1-org.kde.LogoutPrompt.
11:10:23 ksmserver-logout-greeter[496120]: org.kde.Shutdown D-Bus service is already registered; quitting
```

In that login session `im-chooser` was launched exactly once, and that is the
only time in ten days that the shutdown service was activated — while no logout
or shutdown was actually requested. The two events are causally linked by the
code below, not merely correlated in time.

The desktop only recovers after:

```bash
systemctl --user stop 'dbus-:1.1-org.kde.Shutdown'
```

## Cause

`/usr/lib64/libimchooseui.so.0.0.0` (package `im-chooser-common`) implements a
cross-desktop "log out" helper in `egg_sm_client_dbus_kde5_new()`: it builds a
proxy for the KDE session manager and pings it to see whether it exists.

```
8bb1: lea  0x12790(%rip),%r9        # "org.kde.Shutdown"
8bb8: xor  %esi,%esi                # flags = 0  → G_DBUS_PROXY_FLAGS_NONE
8bc4: lea  0x127a1(%rip),%r8        # "/Shutdown"
8bcb: push $0x0                     # cancellable = NULL
8bcd: call g_dbus_proxy_new_for_bus_sync
...
8bf3: lea  0x12739(%rip),%r8        # "Ping"
8bff: lea  0x1273e(%rip),%rcx       # "org.freedesktop.DBus.Peer"
8c1c: call g_dbus_connection_call_sync
```

String table (verified with `strings -a -t x` and the offsets above):

```
12739 Ping
1273e org.freedesktop.DBus.Peer
12790 org.kde.Shutdown
127a1 /Shutdown
```

The proxy is created with flags `0`, i.e. without
`G_DBUS_PROXY_FLAGS_DO_NOT_AUTO_START`. GDBus therefore sends
`StartServiceByName` for `org.kde.Shutdown` as part of creating the proxy, which
activates `plasma-shutdown` — the application only wanted to *check* whether the
session manager exists.

To be explicit: `im-chooser` does **not** call `logout` here. The only remote
call it makes is the harmless `Peer.Ping`. The side effect is purely the
auto-start.

## Expected result

Merely opening (or probing) the chooser must have no effect outside the
application: the KDE shutdown service must not be started unless the user
actually asks to log out.

## Suggested fix

Pass `G_DBUS_PROXY_FLAGS_DO_NOT_AUTO_START` (flag value 4) when creating the
proxy, or better, defer creating the proxy and the `Peer.Ping` probe until an
action that actually needs it is used (for example the *Log Out* button, which
is backed by `imchoose_ui_is_logout_required`). The equivalent probes for
`org.gnome.SessionManager` and `org.xfce.Session.Manager` in the same function
should be reviewed for the same pattern.

## Notes

- Because the KDE side keeps the activated service resident, the visible symptom
  is a dead *Shut Down* entry rather than anything related to input methods,
  which makes this bug hard to attribute from the user's point of view.
- A companion report against KDE (`plasmashell / Session Management`) covers the
  residency of `plasma-shutdown` and the greeter's
  `org.kde.Shutdown D-Bus service is already registered; quitting` behaviour.