fix: prevent WM-managed windows from being embedded during tray restart recovery

[Copilot]

find_unmanaged_icons() was embedding regular application windows (including fullscreen ones) as blank tray icons on restart. The _NET_CLIENT_LIST filter silently became a no-op on any WM that doesn't maintain that property — XInternAtom(..., True) returns None, the fetch is skipped, nclient_wins stays 0, and every window with _XEMBED_INFO passes through unchecked.

Changes

• Add ICCCM WM_STATE filter (primary gate): Skip any window whose WM_STATE is NormalState (1) or IconicState (3). Per the system tray protocol, tray icons must be in WithdrawnState (0) and are never managed by the WM. This works universally — EWMH and non-EWMH WMs alike (i3, bspwm, sway, openbox, etc.).
• Retain _NET_CLIENT_LIST filter (supplementary): Still useful as a secondary guard on EWMH-compliant WMs; now clearly documented as such rather than the sole line of defence.

/* skip windows the WM is actively managing */
if (xa_wm_state != None) {
    rc = x11_get_window_prop32(..., xa_wm_state, xa_wm_state,
                               &wm_state_data, &wm_state_len);
    if (rc == SUCCESS && wm_state_data != NULL) {
        long wm_state = ((long *)wm_state_data)[0];
        XFree(wm_state_data);
        if (wm_state != WithdrawnState) continue;
    }
}

Original prompt

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This section details on the original issue you should resolve

<issue_title>Stalonetray does not find apps in system tray after restarting stalone tray</issue_title>
<issue_description>Describe the bug
If you close stalonetray during a session, say to reconfigure it, and then start it again, apps that were on system tray are no longer visible. However restarting the app, say discord, allows it to show back up in the system tray.

To Reproduce
Steps to reproduce the buggy behavior (even if intermittent):

1. Use bswpwm
2. Launch any app that appears in system tray
3. close then reopen stalonetray
4. See error

Expected behavior
I expect stalonetray to show apps that are in the system tray

Log files
I dont have stalonetray built from source so I currently have no log trace option.
</issue_description>

Comments on the Issue (you are @copilot in this section)

@d3adb5 Can you produce logs now that #58 was merged, @Tomaqa? By the way, if you build stalonetray from source using `meson setup --debug`, you should be able to use the `trace` log level even with 1.0.1.

• Fixes Stalonetray does not find apps in system tray after restarting stalone tray #53

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