feat(dom-widgets): forward middle mouse events to canvas for panning

Add `forwardMiddleMouseToCanvas` utility to forward middle mouse button events from DOM widgets to the ComfyUI canvas, enabling workflow panning when the cursor is over a widget. The function is implemented in `vue-widgets/src/main.ts` and documented in the developer guide. Additionally, fix `getPoolConfigFromConnectedNode` to return null for inactive pool nodes.

web/comfyui/utils.js

@@ -504,6 +504,11 @@ export function getPoolConfigFromConnectedNode(node) {
         return null;
     }
 
+    const isNodeActive = poolNode.mode === undefined || poolNode.mode === 0 || poolNode.mode === 3;
+    if (!isNodeActive) {
+        return null;
+    }
+
     const poolWidget = poolNode.widgets?.find(w => w.name === "pool_config");
     return poolWidget?.value || null;
 }