feat: Implement a UI using the AG-UI standard

[edenreich]

Summary

Implements a user interface using the AG-UI standard for the inference gateway CLI.

Changes

• Added AG-UI standard compliant UI components
• Implemented user interface following AG-UI design patterns
• Updated UI interactions and visual elements

Testing

• UI components follow AG-UI standards
• All interactions work as expected
• Visual consistency maintained

Notes

This PR implements the AG-UI standard for improved user experience and interface consistency.

[edenreich]

Todos

• Fix the reloading of the messages from the database - it currently displays everything in raw format, better would be to preserve consistent styling with collapsible tools
• Implement a progress bar for TodosWrite tool
• Probably extract the UI to a separate repository (the existing UI repository)
• Package the UI as a container - simpler setup

[edenreich]

Closing this as I don't like this approach, will go with a standard PTY session over websockets.

Reason - there are too many duplications which means I'll have to maintain both UI components and TUI components - it simply doesn't scale well.