fix(shell): distinguish between unmapping and destroying surfaces

Previously, `unmap_surface` automatically pushed all unmapped windows
into the `pending_windows` list. This behavior is correct for X11
windows (which may be remapped) but incorrect for Wayland `toplevel_destroyed`
events, where the role is permanently gone.

This caused issues with clients like Telegram that reuse `wl_surface`s.
Because the destroyed toplevel remained in `pending_windows`, a
subsequent cleanup commit (e.g., null buffer) triggered a configure
event. This prematurely marked the surface as `configured` in the
shell state.

Consequently, when the client attached a new `xdg_toplevel` role,
the compositor skipped the mandatory initial configure event (assuming
it was already done), causing the window to never appear.

This refactors `unmap_surface` to return `Option<PendingWindow>`
instead of mutating global state.
- XWayland: Explicitly saves the pending window (behavior preserved).
- XDG Shell: Drops the pending window, preventing ghost state interactions.

Fixes #1816

src/xwayland.rs

@@ -873,7 +873,11 @@ impl XwmHandler for State {
             shell.override_redirect_windows.retain(|or| or != &window);
         } else {
             let seat = shell.seats.last_active().clone();
-            shell.unmap_surface(&window, &seat, &mut self.common.toplevel_info_state);
+            if let Some(pending) =
+                shell.unmap_surface(&window, &seat, &mut self.common.toplevel_info_state)
+            {
+                shell.pending_windows.push(pending);
+            }
         }
 
         let outputs = if let Some(wl_surface) = window.wl_surface() {