🎨 Palette: Improve accessibility of form control groups

[n24q02m]

💡 What: Replaced generic <div role="group"> and <div role="radiogroup"> containers in the popup UI with native HTML <fieldset> elements, updating their pseudo-label <label id="..."> counterparts to semantic <legend> tags.
🎯 Why: Generic grouping roles paired with aria-labelledby often provide an inferior screen reader experience compared to the native <fieldset> and <legend> elements, which are specifically designed to group related form controls natively and robustly across all assistive technologies.
📸 Before/After: No visual changes were introduced. <fieldset> defaults were reset inline to strictly adhere to existing CSS patterns without adding new custom CSS classes.
♿ Accessibility: Vastly improves the context announcement for screen reader users when navigating the 'Operation', 'Execution Mode', and 'Scope' grouped inputs.

---

PR created automatically by Jules for task 2023884202752768058 started by @n24q02m

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None