Address Make app review feedback

[JhumanJ]

Summary

• make the self-hosted base URL immutable and document required token abilities
• cap the forms RPC at 300 results and return an explicit JSON webhook acknowledgement
• align labels, connection metadata, and connection errors with Make guidelines
• add contract coverage for every changed review requirement

Review findings validated separately

• integration_id: make is intentional and accepted by OpnForm's registered MakeIntegration handler
• the handler emits form_id, form_title, form_slug, submission_id, optional edit_link, and data
• trigger mappable parameters remain empty; workspace/form selectors live only on the webhook

Validation

• npm test (10/10 passed)
• JSON parse check for all tracked JSON files
• git diff --check