## What happened

The `SUPER + ALT + comma` keybinding ("Invoke last notification", bound to
`omarchy-shell notifications invokeLast`) does nothing and prints `none`
whenever no notification toast is currently on screen — which is the normal
state, since toasts auto-expire after a few seconds.

## What was expected

The most recent notification is re-shown as a toast — like `showHistory`
replays history, but for the newest entry only — so it can be seen (and its
action invoked) again.

## Steps to reproduce

1. Send a notification (e.g. `notify-send test`), let the toast expire or
   dismiss it.
2. Press `SUPER + ALT + comma`.
3. Nothing appears; `omarchy-shell notifications invokeLast` prints `none`.

Verified live: with 10 archived notifications in
`~/.local/state/omarchy/notifications/history/` and no popup on screen, the IPC
returns `none`.

## Cause

`shell/plugins/notifications/Service.qml`, in the `notifications` IPC handler:

```qml
// Fire the default action on the most recent popup, then dismiss it.
function invokeLast(): string {
  if (popupModel.count === 0) return "none"
  service.invokePopupDefault(0)
  return "ok"
}
```

The guard on `popupModel.count === 0` bails out instead of falling back to the
newest entry in `historyDir` — the same files `showRecentHistory()` replays.

## System

- Omarchy 4.0.0-1 (stable)
- CPU: AMD Ryzen 5 5600X 6-Core Processor
- GPU: AMD Radeon RX 7600 (Navi 33)