[APP] LayerOne Sign

**Name of app / service**
LayerOne Sign — eIDAS / PAdES electronic signature, SMS OTP, audit certificate

**Link to developer documentation**
- OpenAPI spec: https://raw.githubusercontent.com/GOLayerone/layerone-api-specs/main/sign-openapi.yaml
- Developer portal: https://dev.layerone.fr/integrations.html

**Is lack of support preventing you from moving forward, or do you have a workaround?**
We are the API publisher (GO PROTECT / LayerOne). We have already built ready-to-use components following the registry conventions and would like the `sign` app registered so we can contribute them. Authentication is a simple API key sent in the `X-API-Key` header.

**Are there specific actions or triggers you'd like to see for this app?**
send-for-signature, detect-fields, download-signed-document, cancel-document, send-otp, verify-otp, get-document-status, get-audit-certificate, validate-signature (9 actions)