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)

browser_tests/tests/nodeHelp.spec.ts

@@ -553,12 +553,6 @@ This is English documentation.
       )
       await selectNodeWithPan(comfyPage, checkpointNodes[0])
 
-      // Click help button again
-      const helpButton2 = comfyPage.page.locator(
-        '.selection-toolbox button[data-testid="info-button"]'
-      )
-      await helpButton2.click()
-
       // Content should update
       await expect(helpPage).toContainText('Checkpoint Loader Help')
       await expect(helpPage).toContainText(