[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>

tests-ui/tests/renderer/thumbnail/composables/useWorkflowThumbnail.spec.ts

@@ -1,7 +1,10 @@
 import { createPinia, setActivePinia } from 'pinia'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 
-import { ComfyWorkflow, useWorkflowStore } from '@/stores/workflowStore'
+import {
+  ComfyWorkflow,
+  useWorkflowStore
+} from '@/platform/workflow/management/stores/workflowStore'
 
 vi.mock('@/renderer/thumbnail/graphThumbnailRenderer', () => ({
   createGraphThumbnail: vi.fn()
@@ -19,7 +22,7 @@ vi.mock('@/scripts/api', () => ({
 }))
 
 const { useWorkflowThumbnail } = await import(
-  '@/renderer/thumbnail/composables/useWorkflowThumbnail'
+  '@/renderer/thumbnail/useWorkflowThumbnail'
 )
 const { createGraphThumbnail } = await import(
   '@/renderer/thumbnail/graphThumbnailRenderer'