Migrate frontend UI primitives to Nebari design registry

[MUFFANUJ]

Reference Issues or PRs

Closes #439

What does this implement/fix?

Put a x in the boxes that apply

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features not to work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

Testing

• Did you test the pull request locally?
• Did you add new tests?

Documentation

Access-centered content checklist

Text styling

• The content is written with plain language (where relevant).
• If there are headers, they use the proper header tags (with only one level-one header: H1 or # in markdown).
• All links describe where they link to (for example, check the Nebari website).
• This content adheres to the Nebari style guides.

Non-text content

• All content is represented as text (for example, images need alt text, and videos need captions or descriptive transcripts).
• If there are emojis, there are not more than three in a row.
• Don't use flashing GIFs or videos.
• If the content were to be read as plain text, it still makes sense, and no information is missing.

Any other comments?

This PR migrates Nebi’s frontend shadcn setup to the @nebari design registry, replaces the registry-backed UI primitives with Nebari versions, reconciles theme/utils integration, and keeps registry-absent local components explicitly documented. It also updates affected call sites to the new Base UI component APIs while preserving existing behavior and accessibility.

• Added frontend/components.json with the @nebari registry
• Installed/reconciled @nebari/theme in frontend/src/index.css
• Reconciled @nebari/utils with existing cn, capitalize, and getWorkspaceStatusColor
• Replaced registry-backed primitives: button, input, textarea, badge, card, dialog, tabs, select
• Added required registry dependency: spinner
• Kept local-only primitives with notes: alert-dialog, select-v2, split-button, confirm-dialog, user-badge
• Preserved Nebi-specific tokens like --color-primary-hover and --color-nav-hover
• Updated feature components for new Dialog, Tabs, Select, and Button APIs
• Documented the one intentional select ref compatibility exception
• Verified snapshots do not need updates

[netlify]

✅ Deploy Preview for nebi-docs canceled.

Name	Link
🔨 Latest commit	2bf9307
🔍 Latest deploy log	https://app.netlify.com/projects/nebi-docs/deploys/6a84d830ab20340008e7a6b1