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/wayland/handlers/xdg_shell/mod.rs

@@ -321,7 +321,7 @@ impl XdgShellHandler for State {
             let output = shell
                 .visible_output_for_surface(surface.wl_surface())
                 .cloned();
-            shell.unmap_surface(
+            let _ = shell.unmap_surface(
                 surface.wl_surface(),
                 &seat,
                 &mut self.common.toplevel_info_state,