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## Summary by CodeRabbit
- **Bug Fixes**
- Improved code block preview rendering to only display the preview when
appropriate, preventing unwanted previews.
- **Refactor**
- Simplified the HTML preview system by always using a secure
iframe-based approach and removing the WebContainer integration.
- Updated iframe permissions and content delivery for enhanced security
and compatibility.
- **Chores**
- Removed the "Enable Web Container" feature flag and all related
internal logic.
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