Enhance dataset view with improved readability, fallback summary, and keyword matching updates

[elainefan331]

This PR introduces several UI and logic enhancements to improve user experience across the dataset view and summary sections.

New Features

• Added AI Summary Tooltip — Provides contextual explanation for the AI-generated summary section.
• Added Participants Preview Table — Displays participant data in a compact table format for better readability.
• Added Fallback to README Summary — Displays the dataset’s README content as a summary when the AI-generated summary is unavailable.

Enhancements

• Improved Keyword Highlighting — Updated highlightKeyword function to check secondary fields (e.g., Funding, References, Acknowledgements) when no matches are found in visible fields.
• Updated Navigation Button — Replaced the old “Back” button with a Home icon linking to the database path for consistent navigation.