feat(CLI Tool): #3591700 Support `content-entity-reference` props in CLI and Workbench

• adds support for content-entity-reference props in CLI push and pull commands
• adds support for content-entity-reference props in eslint-config and CLI validate command
• adds support for content-entity-reference props previews in Workbench
• adds /canvas/api/v0/ui/content-entity-reference/preview/{entity_type}/{entity} endpoint for providing resolved entityFields expressions against the entity selected for preview
• expands CLI agents-context command to provide context for ai agents to work with content-entity-reference-props

AI-Generated: Yes (Used Codex CLI to iterate over the implementation).

Testing instructions

• npm run build -w @drupal-canvas/cli
• npm run build -w @drupal-canvas/workbench
• npm link --workspaces
• create a test project with npx @drupal-canvas/create -t https://github.com/wotnak/nebula.git -r cer-props - the branch includes skill updates for working with content-entity-reference props
• npm link drupal-canvas @drupal-canvas/cli @drupal-canvas/workbench
• prompt ai agent to create a component with props referencing content entities, for example create component showing selected featured articles (assuming the configured drupal site has article nodes)
• verify that created component has a content-entity-reference prop
• open Workbench npx canvas-workbench and verify that previews for created component work and the entity used for the preview can be selected
• verify that the component passes validation and can be pushed to the site npx canvas push -y
• add the component to a page and save changes
• npx canvas pull -y and verify pulled page includes the cer prop and preview for it is working in Workbench
• verify the same for content templates and global regions
• prompt ai agent to create a new page with the new component and verify that the content-entity-reference prop is correctly added to the page

Closes #3591700