feat: add close button to demo callout to exit mid-demo

[imantsk]

Summary

• Adds an Exit demo (X) button to the top-right of .demo-callout in the Blueprints, Cloud Library and AI Agent demos.
• Clicking it ends the walkthrough the same way Skip animation does, jumping to the closing panel.
• The callout text stays hidden from assistive technology (each stage is already announced by a live region); the close button is exposed with an accessible name.

Testing

• ESLint and Stylelint pass on the changed files; no TypeScript errors in the changed files.
• New Playwright test in tests/e2e/blueprints-demo.spec.ts: starts the demo, clicks Exit demo, and checks that the closing panel appears and the callout is gone.

[code-snippets-bot]

Download and install

📦 code-snippets.4.0.0.zip