[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/composables/useTemplateWorkflows.test.ts

@@ -1,13 +1,16 @@
 import { flushPromises } from '@vue/test-utils'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 
-import { useTemplateWorkflows } from '@/composables/useTemplateWorkflows'
-import { useWorkflowTemplatesStore } from '@/stores/workflowTemplatesStore'
+import { useTemplateWorkflows } from '@/platform/workflow/templates/composables/useTemplateWorkflows'
+import { useWorkflowTemplatesStore } from '@/platform/workflow/templates/repositories/workflowTemplatesStore'
 
 // Mock the store
-vi.mock('@/stores/workflowTemplatesStore', () => ({
-  useWorkflowTemplatesStore: vi.fn()
-}))
+vi.mock(
+  '@/platform/workflow/templates/repositories/workflowTemplatesStore',
+  () => ({
+    useWorkflowTemplatesStore: vi.fn()
+  })
+)
 
 // Mock the API
 vi.mock('@/scripts/api', () => ({