Add action buttons for data export and chart visualization

[Copilot]

Implements download/copy actions for data preview and chart visualization sections as requested in issue #941.

Changes

DataPreview Component

• Removed filter button, retained only download action
• Implemented RFC 4180 compliant CSV export with proper escaping for commas, quotes, and newlines
• Downloads as timestamped file: data_{timestamp}.csv

Visualization Component

• Added hover overlay on chart iframe with Copy and Download buttons
• Copy: Copies chart HTML to clipboard via navigator.clipboard.writeText with 2s success feedback
• Download: Downloads chart HTML as chart_{timestamp}.html
• Styled with glassmorphism effect (backdrop blur, semi-transparent white background, shadow)

Implementation Notes

Helper functions handle:

• CSV generation with value escaping
• Blob creation and URL lifecycle management
• Clipboard API with fallback error handling

Screenshots

Data Preview with Download Button:

Chart Hover State with Action Buttons:

Copy Success Feedback:

Original prompt

This PR addresses issue #941. The goal is to enhance the user interface by implementing the following:

1. Adjust the chart "iframe" in the visualization section to display two action buttons in the top-right corner on hover:
   • Download: When clicked, the chart should be downloadable as an image.
   • Copy: Adds the ability to copy the chart information to the clipboard.
2. Include user-facing visuals hint & customizations

This pull request was created from Copilot chat.

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[github-actions]

🎊 PR Preview 3e5c47e has been successfully built and deployed to https://antvis-AVA-preview-pr-947.surge.sh

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