[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

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

src/scripts/defaultGraph.ts

@@ -1,4 +1,4 @@
-import type { ComfyWorkflowJSON } from '@/schemas/comfyWorkflowSchema'
+import type { ComfyWorkflowJSON } from '@/platform/workflow/validation/schemas/workflowSchema'
 
 export const defaultGraph: ComfyWorkflowJSON = {
   last_node_id: 9,