## What happens

With more than one bar (one per monitor), the pending-update icon shows up on some monitors and not others, and stays that way for up to six hours.

## Why

`SystemUpdate.qml` is instantiated once per bar, and each instance runs `omarchy-update-available` from its own `Timer` with `triggeredOnStart: true`, so every monitor starts one at the same instant. `omarchy-update-available` calls `checkupdates`, which shares one temporary database per user (`${TMPDIR}/checkup-db-${UID}/`) guarded by `db.lck`. When two runs overlap, the loser prints `==> ERROR: Cannot fetch updates` and exits 1. The widget maps that exit code straight to `updateAvailable = false`, so that monitor's bar hides the icon until the next six-hour check.

## Reproduce

```
$ (omarchy-update-available; echo "A=$?") & (omarchy-update-available; echo "B=$?") & wait
omarchy-dev 4.0.0.r2138.gf2b419d-1 -> 4.0.0.r2147.g2fbac0c-1
B=0
Omarchy is up to date
A=1
```

Run alone, it always reports the update. Two monitors, two bars, same result in the UI: the icon appears on one bar only.

## Environment

omarchy-dev 4.0.0.r2138.gf2b419d-1, quickshell 0.3.1-1, three monitors (two with a bar).

## Possible fixes

- Serialize the script with `flock` and cache the result briefly, so all bars see the same answer (what I am running locally).
- Or have a single instance own the check and broadcast the result, since `broadcast` already exists for `refresh`/`clear`.
- Either way, `checkupdates` failing should probably not be indistinguishable from "no updates".

Happy to send a PR for whichever you prefer.