Custom field not appearing in admin UI
### Node Version

20.18.1

### NPM/Yarn/PNPM Version

pnpm 9.15.1

### Strapi Version

5.9.0

### Operating System

Linux (Debian/Ubuntu)

### Database

PostgreSQL

### Javascript or Typescript

Typescript

### Bug Description

When creating a custom field like described the API docs, the custom field / plugin is not recognized. The plugin is attached to this issue. Things I've double-checked already:

- Properly register plugin and custom field, make sure the IDs match
- Compare structure to the online API docs
- Consult console and dev tools
- Review possible TS type- or linting errors

[my-strapi-plugin.zip](https://github.com/user-attachments/files/18724034/my-strapi-plugin.zip)

### Steps to Reproduce

1. Copy the plugin into any Strapi app
2. Try to locate the custom field in the content type builder

### Expected Behavior

Observe the custom field in the content type builder