## What happened

With two bars (one per monitor), the Omarchy update indicator (`omarchy.system-update`) only lights up on **one** screen. Clock, workspaces, tray, etc. show on both.

## Why

`SystemUpdate.qml` starts `omarchy-update-available` from a `Timer { triggeredOnStart: true }` on **every** bar instance at once. That script calls `checkupdates`. Pacman only allows one of those to succeed.

The loser exits non-zero and this line hides the icon on that monitor:

```qml
onExited: function(exitCode) {
  root.updateAvailable = exitCode === 0
}
```

Reproduced on 4.0.3 and 4.0.4: consecutive runs of `omarchy-update-available` flip between “up to date” (exit 1) and a real `omarchy x -> y` line (exit 0).

`BarWidget.broadcast()` already exists because IPC only hits one handler. The timer path does not use it, and even a broadcast of `refresh()` would re-run the same racy check. A success on any instance needs to set `updateAvailable` on **all** peers, and a failure must not clear a peer that already succeeded.

## Repro

1. Two monitors, stock bar, `omarchy.system-update` in the layout.
2. Have a pending `omarchy` package update.
3. Restart the shell (`omarchy restart shell`) so both timers fire together.
4. The circular-arrow icon appears on one bar only.

## Expected

Same as the other bar widgets: the icon on **every** monitor, or a documented single-bar-only widget.

## Environment

- Omarchy 4.0.4-1
- Two 1920×1080 outputs (HDMI-A-1, DP-1)
- Hyprland / omarchy-shell

## Workaround

A cloned widget that, on exit 0, sets `updateAvailable = true` on every `moduleWidgets(...)` instance and ignores a later exit 1 if already true.