[UX] Missing tooltips for toolbar buttons between "Preview" and "Features" in Workflow Editor

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### 1. Is this request related to a challenge you're experiencing? Tell me about your story.

When editing a workflow, I found that several header controls were represented only by icons, including Chat Variables, Environment Variables, Global Variables, and the Checklist. It was not immediately clear what each control did without clicking it, which made the workflow editor harder to discover and use efficiently.


### 2. Additional context or comments

_No response_

### 3. Can you help us with this feature?

- [x] I am interested in contributing to this feature.

Start in the Workflow Editor and locate the header controls between “Preview” and “Features,” especially Chat Variables, Environment Variables, Global Variables, and Checklist. Review how nearby toolbar buttons provide tooltips, then verify that hovering each icon displays a clear label without disrupting the editor.

Written by the indexing model from the issue text.