fix(gui/tray): track watcher loss and never strand the window

The `registered` flag was one-way: set true once the tray registered, but
never cleared if the StatusNotifierWatcher later disappeared (panel restart,
tray plugin disabled, tray app killed). After that, a Wayland close-to-tray
would destroy the window into a tray that no longer exists, with no recovery
short of SIGTERM.

Implement ksni's `watcher_online`/`watcher_offline` callbacks to keep the
shared flag in sync. On offline, also force the window back (idempotent
`show()`) so a window that was already hidden when the watcher died isn't
stranded, and return true to keep the service alive for re-registration.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/gui/tray.rs

@@ -87,6 +87,10 @@ struct PixelPassTray {
     /// Wakes the winit loop and delivers the action — works even when the
     /// window has been dropped to the tray (no egui frame is running then).
     proxy: EventLoopProxy<UserEvent>,
+    /// Shared with [`TrayHandle`]; kept in sync with the watcher's presence via
+    /// the `watcher_online`/`watcher_offline` callbacks so the app never diverts
+    /// a close to a tray that has since disappeared.
+    registered: Arc<AtomicBool>,
 }
 
 impl PixelPassTray {
@@ -131,6 +135,25 @@ impl ksni::Tray for PixelPassTray {
         self.notify(TrayAction::Show);
     }
 
+    /// The StatusNotifierWatcher came back (e.g. the panel restarted). Mark the
+    /// tray live again so close-to-tray can resume hiding the window.
+    fn watcher_online(&self) {
+        self.registered.store(true, Ordering::Release);
+    }
+
+    /// The watcher went away (panel restart, tray plugin disabled, …). Clear the
+    /// flag so a subsequent close quits normally instead of destroying the window
+    /// into a tray that no longer exists, and force the window back now in case
+    /// it was already hidden (otherwise it'd be stranded with no way to restore).
+    /// Returning `true` keeps the service alive so it re-registers if the watcher
+    /// returns.
+    fn watcher_offline(&self, reason: ksni::OfflineReason) -> bool {
+        tracing::warn!("tray: StatusNotifierWatcher offline ({reason:?}); restoring window");
+        self.registered.store(false, Ordering::Release);
+        self.notify(TrayAction::Show);
+        true
+    }
+
     fn menu(&self) -> Vec<ksni::MenuItem<Self>> {
         use ksni::menu::{MenuItem, StandardItem};
         vec![
@@ -202,6 +225,7 @@ pub fn start(proxy: EventLoopProxy<UserEvent>) -> Option<TrayHandle> {
                     status: TrayStatus::Idle,
                     icon,
                     proxy,
+                    registered: registered_thread.clone(),
                 };
                 let handle = match tray.spawn().await {
                     Ok(handle) => handle,