[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/useCoreCommands.test.ts

@@ -49,7 +49,7 @@ vi.mock('firebase/auth', () => ({
   onAuthStateChanged: vi.fn()
 }))
 
-vi.mock('@/services/workflowService', () => ({
+vi.mock('@/platform/workflow/core/services/workflowService', () => ({
   useWorkflowService: vi.fn(() => ({}))
 }))
 
@@ -69,7 +69,7 @@ vi.mock('@/stores/toastStore', () => ({
   useToastStore: vi.fn(() => ({}))
 }))
 
-vi.mock('@/stores/workflowStore', () => ({
+vi.mock('@/platform/workflow/management/stores/workflowStore', () => ({
   useWorkflowStore: vi.fn(() => ({}))
 }))