feat(theme): add Banner Component

[SoonIter]

Summary

feat(theme): add Banner Component

Related Issue

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[Copilot]

Pull Request Overview

This PR introduces a new Banner component to the theme system, replacing the previous Announcement component with a more flexible and integrated solution. The Banner component includes persistent dismissal via storage, customizable content, and proper height integration with the navigation system.

Key Changes:

• Adds a new Banner component with storage-based dismissal functionality and dynamic height calculation
• Updates all layout styles to account for banner height using CSS custom properties
• Replaces the external Announcement component with the new Banner in the website theme

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
packages/theme-default/src/components/Banner/index.tsx	Implements new Banner component with forwardRef, storage management, and dynamic height tracking
packages/theme-default/src/components/Banner/index.scss	Adds styling for banner with gradient background and close button
packages/theme-default/src/logic/mergeRefs.ts	Utility function to merge multiple React refs
packages/theme-default/src/index.ts	Exports new Banner component and mergeRefs utility
website/theme/index.tsx	Replaces Announcement component with Banner and removes NoSSR wrapper
packages/theme-default/src/layout/DocLayout/index.scss	Updates layout calculations to include banner height
packages/theme-default/src/components/Nav/index.scss	Adjusts nav positioning to account for banner
packages/theme-default/src/components/NavScreen/index.scss	Updates screen positioning for banner height

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