view_surface_at: skip shaded windows in pointer hit-testing

When a window is shaded (rolled up to titlebar only), the client surface
is hidden but view_surface_at would still return it for points over the
frame decorations. This caused two symptoms:

1. Pointer focus stayed on the client surface, showing I-beam cursor
   instead of default arrow over the titlebar.
2. Button events routed to the client surface instead of titlebar,
   preventing double-click-to-unshade from working.

Fix: after matching a toplevel view via scene graph, check whether the
associated WWindow has flags.shaded set and skip it if so.

src/backend/wayland/wl_pointer_focus.c

@@ -64,6 +64,19 @@ view_surface_at(int px, int py, double *sx_out, double *sy_out,
         }
         if (!match) continue;
 
+        /* If the window is shaded, the client surface is hidden;
+         * do not route pointer events to it.  The pointer is over
+         * frame decorations (titlebar) regardless of what the scene
+         * graph or xdg geometry says. */
+        {
+            WObjDescriptor *_desc = wm_backend->context_find(v->id, WM_CTX_CLIENT_WIN);
+            if (_desc && _desc->parent_type == WCLASS_WINDOW) {
+                WWindow *_wwin = (WWindow *)_desc->parent;
+                if (_wwin->flags.shaded)
+                    continue;
+            }
+        }
+
         if (v->xw_surface && v->xw_surface->surface) {
             double sx = px - (double)v->x;
             double sy = py - (double)v->y;