### What happened

The bar recolors its own glyphs to stay legible when transparency is toggled,
but tray icons are only tinted when the icon name ends in `-symbolic`. Apps
that advertise a non-symbolic icon name are rendered as-is, so they cannot
follow the bar foreground and are unreadable in one of the two bar states.

From `shell/plugins/bar/widgets/Tray.qml`:

```qml
// Symbolic icons ship a fixed fill (often near-white) that the host is meant
// to recolor to its foreground; detect them by the freedesktop "-symbolic"
// name suffix so they can be tinted instead of rendered as-is.
function iconIsSymbolic(icon) {
  var name = String(icon || "").split("?")[0]
  return name.slice(-9) === "-symbolic"
}
```

Both tray items on this machine fail that test:

```
nm-applet   IconName = "nm-device-wired"
steam       IconName = "steam_tray_mono"
            IconThemePath = ~/.local/share/Steam/public
```

`nm-applet` is not niche — it is autostarted system-wide by
`/etc/xdg/autostart/nm-applet.desktop` from `network-manager-applet`.

This compounds the icon-theme mismatch filed separately: with a light icon
set on a dark bar the icons are invisible, and with a dark icon set they are
invisible in transparent mode over a light wallpaper. There is no icon-theme
choice that works for both bar states, because the icon is static and the
backdrop is not.

### Expected

Some fallback for non-symbolic tray icons. A few options, roughly in order of
effort:

1. Treat a monochrome icon as tintable regardless of name — many apps ship a
   single-color tray icon without following the `-symbolic` convention
   (`steam_tray_mono` literally says "mono").
2. Prefer a `-symbolic` variant when the icon theme provides one for the
   requested name, before falling back to the literal name.
3. Draw a subtle backdrop chip behind untintable tray icons in transparent
   mode, so they keep contrast without being recolored.

### Steps to reproduce

1. `omarchy theme set nord`
2. Ensure an app with a non-symbolic tray icon is running (`nm-applet` is
   autostarted on most installs).
3. Expand the bar's system tray. The icon is dark-on-dark.
4. Override the icon theme to the dark variant:
   `echo "Yaru-blue-dark" > ~/.config/omarchy/themes/nord/icons.theme && omarchy theme set nord`
5. The icon is now legible on the solid dark bar.
6. Double-click the bar to enable transparency over a light wallpaper. The
   same icon is now light-on-light and unreadable.

The bar's own font glyphs remain legible throughout, which is the contrast
that makes the gap obvious.

### System

- Omarchy 4.0.1-1 (upgraded from 3.x via omarchy-upgrade-to-quattro)
- Kernel 7.1.9-arch1-2
- AMD Ryzen 5 5600X, NVIDIA RTX 2060 (TU106), nvidia-open-dkms
- Single 1920x1080 display, scale 1