Add sign in modal and overlay to obscure content until Auth0

[brothhammer]

Brief Description

Place the Storybook manager logout control in the left sidebar under the search.

JIRA Link

Related Issue

General Notes

• Add manager-side code to render a logout control in the Storybook sidebar instead of the top toolbar.
• Create a dedicated DOM container (#sb-manager-logout-container) and append the logout button (#sb-manager-logout-dom) there.
• Use a MutationObserver and re-placement logic to keep the control correctly positioned across Storybook re-renders.
• Add CSS to force block/full-width layout and spacing so the logout button doesn’t crowd the search input.

Motivation and Context

We want to get a better idea of who is accessing the Astro components.

Issues and Limitations

• Placement relies on current Storybook DOM selectors. If Storybook changes these in future versions, updates will be needed.
• implementation defends against re-renders via MutationObserver, aggressive re-parenting by any other scripts could cause issues.

Types of changes

• [ ] Bug fix
• [x] New feature
• [ ] Breaking change

Checklist

• [ ] This PR adds or removes a Storybook story.
• [ ] I have added tests to cover my changes.
• [x] Regressions are passing and/or failures are documented
• [x] Changes have been checked in evergreen browsers

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