[refactor] Migrate litegraph imports from npm package to local subtree

- Updated all imports from '@comfyorg/litegraph' to '@/lib/litegraph/src/'
- Replaced deep dist imports with direct source paths
- Updated CSS import in main.ts
- All imports now use the @ alias consistently

tests-ui/tests/widgets/domWidget.test.ts

@@ -1,6 +1,6 @@
-import { LGraphNode } from '@comfyorg/litegraph'
 import { describe, expect, test, vi } from 'vitest'
 
+import { LGraphNode } from '@/lib/litegraph/src/litegraph'
 import { ComponentWidgetImpl, DOMWidgetImpl } from '@/scripts/domWidget'
 
 // Mock dependencies