HTML artifacts can read other artifacts via getArtifact() and attachments.
When any artifact is created, updated, rewritten, or deleted, all HTML
artifacts now automatically reload to reflect the latest data.
Changes:
- Add reloadAllHtmlArtifacts() method to ArtifactsPanel
- Call reload after all artifact mutations (create/update/rewrite/delete)
- Make HtmlArtifact.sandboxIframeRef and executeContent() public
- Update runtime providers before re-executing HTML content
This ensures HTML artifacts always display current data from their dependencies.