feat(web): add /admin preview console so Craig can see admin UI on iPad #4101

Originally written by @ccantynz-alt on GitHub.
Imported from https://github.com/ccantynz-alt/AlecRae.com/pull/30

The standalone admin sub-app at apps/admin (admin.alecrae.com) is code-complete but won't be reachable until DNS + backend are provisioned. Until then, Craig literally couldn't see an admin page from his iPad.

Add a brand-correct preview at apps/web/app/admin that mirrors the admin app's information architecture:

• 6 KPI tiles (sent, delivery rate, bounce rate, queue, accounts, MRR)
• Recent activity feed with stub rows
• Launch gates checklist (code done vs Craig infra pending)
• Section navigation tiles linking to admin.alecrae.com sub-routes
• Ivory + Italianno wordmark, hairline rules — same brand language as /
• Responsive 1/2/3/6-col grids tuned for iPad

Server-rendered (no client JS), robots-disallowed, builds clean (23/23 static pages, 139 B route + 102 kB shared).

https://claude.ai/code/session_016BVFyXkeASY7sgKAoxHLPK

Description

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactor (no functional changes)
• Documentation update
• Infrastructure / CI change

Testing

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed

Checklist

• My code follows the project style guidelines
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or my feature works
• New and existing tests pass locally (bun run test)
• Lint and type-check pass (bun run lint && bun run typecheck)
• I have updated documentation where necessary

Breaking changes

N/A

Screenshots

N/A