refactor: move renderer-dependent utils into workbench scope (#6621)

This PR cleans up the base-layer utilities so they no longer pull
renderer or workbench code. The renderer-only `isPrimitiveNode` guard
now lives in `src/renderer/utils/nodeTypeGuards.ts`, and the node
help/model/ordering helpers have moved into `src/workbench/utils`. All
affected services, stores, scripts, and tests were updated to import
from the new locations.

The idea is to reduce the number of Base→Renderer/Base→Workbench edges
(higher scoped base/common utils should not import from
renderer/workbench layers).

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6621-refactor-move-renderer-dependent-utils-into-workbench-scope-2a36d73d36508167aff0fc8a22202d7f)
by [Unito](https://www.unito.io)

src/scripts/app.ts

@@ -78,7 +78,7 @@ import {
   findLegacyRerouteNodes,
   noNativeReroutes
 } from '@/utils/migration/migrateReroute'
-import { getSelectedModelsMetadata } from '@/utils/modelMetadataUtil'
+import { getSelectedModelsMetadata } from '@/workbench/utils/modelMetadataUtil'
 import { deserialiseAndCreate } from '@/utils/vintageClipboard'
 
 import { type ComfyApi, PromptExecutionError, api } from './api'