Generic JSON editor fallback UI for arbitrary blueapi plan that failed UI generation

UIFallback in @atlas/blueapi-ui simply says 'UI unavailable'. This should be a JSON text editor, ideally with an initial object derived from the plan's schema. The ErrorBoundary should then be moved to wrap the JsonForms component only, so that the plan name, description, and submission buttons are still rendered.

Start by locating UIFallback in @atlas/blueapi-ui and trace how the failed plan schema reaches it. Review the ErrorBoundary and JsonForms rendering path, then make the fallback provide a JSON text editor with an initial schema-derived object while keeping the plan name, description, and submission buttons visible. Done means arbitrary plans with failed UI generation remain editable and submittable.

Written by the indexing model from the issue text.