### System details

AMD Ryzen AI 7 350 / Radeon 860M, Omarchy 4.0.0-1, kernel 7.1.8-arch1-3, pacman-contrib 1.13.1-1

### What's wrong?

`bin/omarchy-update-available` is not safe to run concurrently. A second
overlapping invocation reports **"Omarchy is up to date" and exits 1** even
though an update is pending.

This matters because the bar calls it once per monitor: `omarchy.system-update`
is an ordinary bar widget, so each monitor's bar instantiates its own copy, and
each copy runs its own `Process` on the same `triggeredOnStart` timer. On a
multi-monitor machine the two checks fire together and one of them loses. Since
the widget is `visible: updateAvailable`, the loser silently renders nothing —
an available update shows no icon at all on that bar.

**Reproduce** (an update must actually be pending):

```
$ for i in 1 2; do (out=$(omarchy-update-available 2>&1); echo "run$i: exit=$? | $out") & done; wait
run2: exit=1 | Omarchy is up to date
run1: exit=0 | omarchy 4.0.0-1 -> 4.0.2-1
```

**Cause.** `checkupdates` (pacman-contrib) syncs into one shared temp database,
`${TMPDIR:-/tmp}/checkup-db-${UID}`, and removes `db.lck` from a
`trap ... INT TERM EXIT`. Two concurrent runs share that directory, so whichever
finishes first drops the other's lock; the loser's `pacman -Sy` fails, or its
`pacman -Qu` reads a half-synced database and prints nothing. Both pacman calls
are `&> /dev/null` / `2> /dev/null`, so the error is invisible, and
`omarchy-update-available` maps the empty result to "up to date":

```bash
update=$(checkupdates --nocolor 2>/dev/null | awk -v package="$package" '$1 == package { print; exit }' || true)
```

A false "up to date" is the bad direction to fail in — it hides a pending
update rather than showing a spurious one.

**Expected:** concurrent callers agree, and a pending update is reported by all
of them.

**Suggested fix:** serialize the script under `flock`, so every caller benefits
rather than only the bar. Per-instance `CHECKUPDATES_DB` would also avoid the
shared directory, but it multiplies the pacman sync by the number of monitors.

Not reported as a display bug on purpose: the missing icon is the visible
symptom, but it is transient — a later refresh can bring it back on both bars —
and the script-level race above is the part that reproduces deterministically.