Sync node help with selection and add watcher tests (#7105)

## Summary
- add a watcher to sync the node help panel with the currently selected
node
- add unit coverage for help auto-switching and guard cases

## Testing
- pnpm typecheck
- pnpm lint:fix
- pnpm exec vitest
tests-ui/tests/composables/graph/useSelectionState.test.ts

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7105-Sync-node-help-with-selection-and-add-watcher-tests-2bd6d73d36508140b5acd3f3c65c5680)
by [Unito](https://www.unito.io)

tests-ui/tests/composables/graph/useSelectionState.test.ts

@@ -1,6 +1,7 @@
 import { createPinia, setActivePinia } from 'pinia'
 import { beforeEach, describe, expect, test, vi } from 'vitest'
-import { type Ref, ref } from 'vue'
+import { ref } from 'vue'
+import type { Ref } from 'vue'
 
 import { useSelectionState } from '@/composables/graph/useSelectionState'
 import { useNodeLibrarySidebarTab } from '@/composables/sidebarTabs/useNodeLibrarySidebarTab'