kdeconnect: disabled notifications plugin logged as ERROR on every device query

DMS logs an error when a paired KDE Connect device has the notifications plugin disabled:

```
Aug 24 15:58:36 homePC dms[1037]: ERROR go: DMS API Error: id=1787579934321 error=dbus call failed: No such object path '/modules/kdeconnect/devices/e489f2a8_6ebb_411c_bd9f_bb77e4469cf4/notifications'
```

Cause: `~/.config/kdeconnect//config` has `kdeconnect_notificationsEnabled=false`, so kdeconnectd never exports the `/notifications` object path. `busctl --user tree org.kde.kdeconnect` shows battery, clipboard, sms, telephony and others, but no `notifications`. DMS calls it anyway.

Everything else about KDE Connect works. Per-plugin availability is normal, so an absent optional path shouldn't be an ERROR.

Suggestion: check `isPluginEnabled("kdeconnect_notifications")` (or `loadedPlugins`) on the device object before calling, and demote "No such object path" to debug.

dms v1.5.0-203-gc67b1850 (Arch, dms-shell-git)

Start at the KDE Connect device-query entry point that calls the notifications object path, using isPluginEnabled("kdeconnect_notifications") or loadedPlugins as the issue suggests. Reproduce with notifications disabled and confirm the query no longer logs an ERROR for the absent path while other KDE Connect plugins continue to work.

Written by the indexing model from the issue text.