[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/components/graph/selectionToolbox/ColorPickerButton.spec.ts

@@ -7,8 +7,8 @@ import { createI18n } from 'vue-i18n'
 
 // Import after mocks
 import ColorPickerButton from '@/components/graph/selectionToolbox/ColorPickerButton.vue'
+import { useWorkflowStore } from '@/platform/workflow/management/stores/workflowStore'
 import { useCanvasStore } from '@/renderer/core/canvas/canvasStore'
-import { useWorkflowStore } from '@/stores/workflowStore'
 
 // Mock the litegraph module
 vi.mock('@/lib/litegraph/src/litegraph', async () => {

src/components/graph/selectionToolbox/ColorPickerButton.vue

@@ -62,8 +62,8 @@ import {
   LiteGraph,
   isColorable
 } from '@/lib/litegraph/src/litegraph'
+import { useWorkflowStore } from '@/platform/workflow/management/stores/workflowStore'
 import { useCanvasStore } from '@/renderer/core/canvas/canvasStore'
-import { useWorkflowStore } from '@/stores/workflowStore'
 import { useColorPaletteStore } from '@/stores/workspace/colorPaletteStore'
 import { adjustColor } from '@/utils/colorUtil'
 import { getItemsColorOption } from '@/utils/litegraphUtil'