### What happened

Launching an app from the menu occasionally leaves a persistent
**"Launching <app>…"** overlay on screen. The app itself starts and works
normally; the overlay never goes away and must be dismissed manually with
`omarchy-shell osd close`.

Seen twice on this machine with different apps (Nautilus and Remmina), both of
which take roughly two seconds to map their first window.

### Cause

`shell/services/AppLibrary.qml` shows and hides the OSD with two *independent*
detached commands, and tracks its own idea of whether the OSD is open:

```qml
// launchDelay, interval: 2000
onTriggered: {
  if (root.toplevelCount() > root.launchToplevelCount || ...) return
  root.launchOsdOpen = true
  Quickshell.execDetached(["omarchy-shell", "osd", "show", ...duration: 0...])
}

function closeLaunchFeedback(serial) {
  ...
  if (root.launchOsdOpen) {                       // <-- guard
    Quickshell.execDetached(["omarchy-shell", "osd", "close"])
    root.launchOsdOpen = false
  }
}
```

If the window appears in the narrow interval around the 2000 ms mark, the two
commands race:

1. `launchDelay` fires, sets `launchOsdOpen = true`, and spawns `osd show`
   with `duration: 0` (no self-expiry).
2. The toplevel appears, `maybeFinishLaunchFeedback()` →
   `closeLaunchFeedback()` runs and spawns `osd close`.
3. The two detached processes reach the shell out of order: **close is
   processed before show**. The OSD ends up visible, with no expiry.
4. `closeLaunchFeedback()` has already set `launchOsdOpen = false` and stopped
   `launchTimeout`, so the 15 s safety net never fires — and even if it did,
   the `if (root.launchOsdOpen)` guard would skip the close.

The result is a permanent overlay. Apps whose first window maps at ~2 s hit
this repeatedly; faster or slower apps never do.

### Expected

The overlay should always disappear once the window is up.

### Suggested fix

Any one of:

- make the `launchTimeout` close unconditional (drop the `launchOsdOpen`
  guard), so a stuck overlay self-heals after 15 s; and/or
- give the OSD a non-zero `duration` so it expires by itself; and/or
- serialise show/close through one ordered channel instead of two detached
  `execDetached` calls, so they cannot be reordered.

### Steps to reproduce

Hard to trigger on demand because it depends on timing, but:

1. Launch an app whose first window maps about 2 s after start (Remmina and
   Nautilus both do on this hardware) from the Omarchy menu.
2. Repeat a handful of times.
3. Occasionally the "Launching …" overlay stays on screen indefinitely;
   `omarchy-shell osd close` clears it.

### System

- Omarchy 4.0.4-1, omarchy-settings 4.0.4-1
- Quickshell 0.3.1-1
- Kernel 7.2.5-3-omarchy
- CPU Intel Core i7-7Y75 / GPU Intel HD Graphics 615
- Google Pixelbook (Eve)