## Cloning the `bar` shell plugin breaks the entire bar with no fallback

**Omarchy version:** 4.0.0-1
**Hyprland:** 0.56.2

### What happened
Running `omarchy plugin clone omarchy.bar` and switching to the clone (`omarchy bar use <clone-id>`) makes the bar disappear completely — no layer surface is created at all (`hyprctl layers` shows nothing under the `omarchy-bar` namespace). This reproduces with a **byte-identical, unmodified copy** of `Bar.qml` — it is not caused by editing the clone.

### Root cause
`pluginBarLoader` in `/usr/share/omarchy/shell/shell.qml` fails to load the cloned bar's QML (`status === Loader.Error`). Its `onStatusChanged` handler is supposed to fall back to the default bar:

```qml
onStatusChanged: {
  if (status === Loader.Error) {
    var detail = errorString && errorString() ? errorString() : ""
    console.warn("bar option " + shell.activeBarId + " failed to load, falling back to " + shell.defaultBarId + ":", detail)
    shell.failedBarId = shell.activeBarId
  }
}
```

`errorString` is referenced as a bare identifier instead of `pluginBarLoader.errorString()` (or similar), so this throws `ReferenceError: errorString is not defined` (confirmed in the shell log) before `shell.failedBarId` is ever set. Because the fallback assignment never runs, `activeBarId` stays pointed at the broken custom bar forever, `defaultBarLoader` stays inactive, and the bar silently vanishes with no visible error to the user.

### Steps to reproduce
```bash
omarchy plugin clone omarchy.bar
omarchy bar use <clone-id>   # e.g. kesav.bar
```
Then check:
```bash
hyprctl layers   # omarchy-bar namespace is missing entirely
journalctl --user -t omarchy-shell -n 50 --no-pager | grep -i "errorString\|shell.qml"
# WARN scene: @shell.qml[256:-1]: ReferenceError: errorString is not defined
```

### Expected
Either the clone loads correctly (the underlying load failure for a cloned first-party `bar`-kind plugin is itself worth investigating), or — at minimum — the `Loader.Error` fallback in `shell.qml` should actually execute so the user gets the default bar back with a warning, instead of a blank bar with no on-screen indication anything is wrong.

### Workaround
`omarchy bar use omarchy.bar` restores the bar immediately.