Test inbound API endpoints from the studio editor

Apps that receive content via inbound APIs (like Presentation Hub) can now reveal their endpoint and bearer token directly from the studio preview. Previously the in-app settings button was a silent no-op in the editor, forcing creators to publish before they could test ingestion. The dialog is also hardened against stalled requests with a 15-second timeout, an actionable error message, and a retry button instead of an infinite spinner.