[CodeHealth] Remove remaining uses of global app var (#3868)

src/composables/widgets/useImagePreviewWidget.ts

@@ -8,6 +8,7 @@ import type {
 import type { InputSpec } from '@/schemas/nodeDef/nodeDefSchemaV2'
 import { calculateImageGrid } from '@/scripts/ui/imagePreview'
 import { ComfyWidgetConstructorV2 } from '@/scripts/widgets'
+import { useCanvasStore } from '@/stores/graphStore'
 import { useSettingStore } from '@/stores/settingStore'
 import { is_all_same_aspect_ratio } from '@/utils/imageUtil'
 
@@ -16,7 +17,7 @@ const renderPreview = (
   node: LGraphNode,
   shiftY: number
 ) => {
-  const canvas = app.canvas
+  const canvas = useCanvasStore().getCanvas()
   const mouse = canvas.graph_mouse
 
   if (!canvas.pointer_is_down && node.pointerDown) {