Move the existing web folder to web/vanilla and update Dockerfile.

[ayao227]

We would like to have the project structure like this:

     lance-data-viewer/
     ├── web/
     │   ├── vanilla/         # Move current HTML/CSS/JS version here
     │   └── react/           # New React app with TypeScript + Material-UI

This PR updates the restructure of existing files

• Moved current web/* files to web/vanilla/
• Updated backend to serve from web/vanilla initially
• Updated Dockerfile.