🚀 Feature: Track potential downstream Formatly adopters

## Feature Request Checklist

- [x] I have pulled the latest `main` branch of the repository.
- [x] I have [searched for related issues](https://github.com/JoshuaKGoldberg/formatly/issues?q=is%3Aissue) and found none that matched my issue.

## Overview

Create a public tracker for downstream projects that may be good candidates for adopting Formatly.

This can serve both as a list of potential users and as a transparent record of outreach made to their maintainers. Inclusion here should mean only that a project appears to have a relevant use case and has been contacted—not that its maintainers have agreed to adopt Formatly.

Good candidates are generally developer tools that generate user-owned files and currently depend directly on a particular formatter to format those files.

## Current candidates

- [ ] Panda CSS (`@pandacss/node`) — [chakra-ui/panda#3691](https://github.com/chakra-ui/panda/issues/3691)
- [ ] React Router (`@react-router/dev`) — [remix-run/react-router#15347](https://github.com/remix-run/react-router/issues/15347)

Additional candidates and links to any downstream discussions or issues can be added here over time.

Start by reviewing the repository's existing public documentation or project-tracking locations to determine where a downstream-adopters tracker belongs. Record the listed Panda CSS and React Router candidates with their outreach links, and ensure the tracker distinguishes contacted projects from confirmed adopters; the issue is done when those entries and future additions have a clear public home.

Written by the indexing model from the issue text.