Fix: Opening mask editor on context menu (#6825)

## Summary

Fix issue of opening mask editor on context menu, reported in
https://github.com/Comfy-Org/ComfyUI_frontend/issues/6824

## Screenshots (if applicable)


https://github.com/user-attachments/assets/666d2769-d848-4b08-b54b-0cf5ed799b35

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6825-Fix-Opening-mask-editor-on-context-menu-2b36d73d3650810781a3c25a23ba488a)
by [Unito](https://www.unito.io)

src/composables/maskeditor/useMaskEditor.ts

@@ -0,0 +1,48 @@
+import type { LGraphNode } from '@/lib/litegraph/src/LGraphNode'
+import { useDialogStore } from '@/stores/dialogStore'
+import TopBarHeader from '@/components/maskeditor/dialog/TopBarHeader.vue'
+import MaskEditorContent from '@/components/maskeditor/MaskEditorContent.vue'
+
+export function useMaskEditor() {
+  const openMaskEditor = (node: LGraphNode) => {
+    if (!node) {
+      console.error('[MaskEditor] No node provided')
+      return
+    }
+
+    if (!node.imgs?.length && node.previewMediaType !== 'image') {
+      console.error('[MaskEditor] Node has no images')
+      return
+    }
+
+    useDialogStore().showDialog({
+      key: 'global-mask-editor',
+      headerComponent: TopBarHeader,
+      component: MaskEditorContent,
+      props: {
+        node
+      },
+      dialogComponentProps: {
+        style: 'width: 90vw; height: 90vh;',
+        modal: true,
+        maximizable: true,
+        closable: true,
+        pt: {
+          root: {
+            class: 'mask-editor-dialog flex flex-col'
+          },
+          content: {
+            class: 'flex flex-col min-h-0 flex-1 !p-0'
+          },
+          header: {
+            class: '!p-2'
+          }
+        }
+      }
+    })
+  }
+
+  return {
+    openMaskEditor
+  }
+}