[refactor] Improve workflow domain organization (#5584)

* [refactor] move workflow domain to its own folder

* [refactor] Fix workflow platform architecture organization

- Move workflow rendering functionality to renderer/thumbnail domain
- Rename ui folder to management for better semantic clarity
- Update all import paths to reflect proper domain boundaries
- Fix test imports to use new structure

Architecture improvements:
- rendering → renderer/thumbnail (belongs with other rendering logic)
- ui → management (better name for state management and UI integration)

This ensures proper separation of concerns and domain boundaries.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

* [fix] Resolve circular dependency between nodeDefStore and subgraphStore

* [fix] Update browser test imports to use new workflow platform paths

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/stores/nodeDefStore.ts

@@ -292,9 +292,9 @@ export const useNodeDefStore = defineStore('nodeDef', () => {
   const showDeprecated = ref(false)
   const showExperimental = ref(false)
   const nodeDefFilters = ref<NodeDefFilter[]>([])
-  const subgraphStore = useSubgraphStore()
 
   const nodeDefs = computed(() => {
+    const subgraphStore = useSubgraphStore()
     return [
       ...Object.values(nodeDefsByName.value),
       ...subgraphStore.subgraphBlueprints