Redirect App

As a business owner I would like to have assurances that my redirect is exactly as I expect so that I am not surprised when I accidentally take my homepage down.

## Context
It's far too easy to accidentally type something into a sheet. Permissions help a bit. Preview / publish flow also helps, but there's no confirmation dialog saying, "this is the redirect you are setting." nor is there anything telling you what is new. If you show up to the sheet, it's difficult to know what has been changed, but not previewed or published.

## Criteria of acceptance
1. A new redirects app.
2. The app has a source and location text field.
3. You can type in the first text field and we try to find any existing redirects that are already in place.
4. If you click on existing, you can change the existing.
5. If you do net-new, you fill in the details.
6. There is a confirmation dialog.
7. Ability to preview and publish.
8. Should support 65,000+ redirects.

The issue names no files, tests, or entry points. Start by locating the existing sheet, preview/publish flow, and redirect handling, then clarify the design and implementation scope for the redirects app, including lookup, editing, confirmation, preview, publishing, and support for 65,000+ redirects.

Written by the indexing model from the issue text.