fix(canvas): keep card drags alive on logos and pan with the middle mouse button

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

resources/css/app.css

@@ -6156,6 +6156,12 @@ html.dark .canvas-zoom-max {
     background-image: var(--canvas-dots-image);
 }
 
+/* A pan (canvas-core panZoom), also a middle-button pan that started on a card. */
+:is([data-ec-viewport], .cv-viewport).panning,
+:is([data-ec-viewport], .cv-viewport).panning * {
+    cursor: grabbing !important;
+}
+
 /* "Floating" navigation (Appearance → Navigation style): the top bar, sidebar,
    tab strip, and settings rail float as framed panels over a dotted backdrop,
    like the canvas islands. Set on <html> by applyStoredTheme() from