feat: Implement CRDT-based layout system for Vue nodes

Major refactor to solve snap-back issues and create single source of truth for node positions:

- Add Yjs-based CRDT layout store for conflict-free position management
- Implement layout mutations service with clean API
- Create Vue composables for layout access and node dragging
- Add one-way sync from layout store to LiteGraph
- Disable LiteGraph dragging when Vue nodes mode is enabled
- Add z-index management with bring-to-front on node interaction
- Add comprehensive TypeScript types for layout system
- Include unit tests for layout store operations
- Update documentation to reflect CRDT architecture

This provides a solid foundation for both single-user performance and future real-time collaboration features.

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

package.json

@@ -115,6 +115,7 @@
     "vue-i18n": "^9.14.3",
     "vue-router": "^4.4.3",
     "vuefire": "^3.2.1",
+    "yjs": "^13.6.27",
     "zod": "^3.23.8",
     "zod-validation-error": "^3.3.0"
   }