Agentic UI: Add preview sites to site overview

[shaunandrews]

Related issues

• None.

How AI was used in this PR

Codex helped extract Preview sites from the larger overview exploration into a focused stacked change, then supported the later design iterations represented by the top integration PR. I reviewed the resulting diff and rendered states.

Proposed Changes

This is the second PR in the site-management UI stack:

1. Agentic UI: Add Connections to site overview #4474 — Connections on the overview
2. Agentic UI: Add preview sites to site overview #4483 — Preview sites on the overview (this PR)
3. Design Exploration: Replace the site dropdown with a permanent site header #4400 — Persistent site header with Share and Sync dialogs
4. Agentic UI: Integrate the site overview, sharing, and sync progress #4601 — Integrated overview polish, reusable sharing controls, and operation progress

This layer makes temporary shareable sites visible and manageable from Overview.

• List previews belonging to the current local site.
• Distinguish active and expired previews and show their remaining lifetime.
• Provide direct publish, open, copy, update/republish, and overflow actions.
• Cover empty, loading, signed-out, offline, active, and expired states.

The top stack layer (#4601) carries the final action labels and ordering, deletion and bulk expired cleanup, footer creation action, live publishing progress, and the reusable list shared with the Share dialog.

Current UI

Testing Instructions

1. Open a site's Overview while signed in.
2. Confirm Preview sites appears after Connections.
3. Check active, expired, empty, and loading states.
4. Exercise publish, open, copy, update/republish, and overflow actions.
5. Verify offline-disabled behavior and both light and dark appearances.

Verification used while preparing this stack:

• Built this exact PR head with the local browser UI target.
• Rendered it against the local Studio backend and captured the screenshot above.
• The focused overview and preview-query tests and full typecheck pass on the integrated stack head.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?