Large update to the visualizer UI

[kazuhidelee]

Description

Summary:
Updating the overall UI for the gittuf visualizer to reduce the vibe-code ness and make the UI/UX experience similar to microsoft Visio / lucid chart style interfaces.

Detailed changes:

• updated the frontend Docker setup so local UI changes can reflect dynamically during development instead of requiring a full restart (updates to startup instruction on readme accordingly)
• update the starting/welcome screen of the visualizer.
• update the visualizer using a graph canvas style UI.
• Make the graph interactive (can be removed, moved around)
• Enable users to compare commit history and view the policy change over the commit
• Enable user to compare versions of policy
• Enable users to simulate/query the policy to inspect which user's approval is needed for a specific policy

currently all the frontend is interacting with a mock data instead of the backend

AI Usage

• I did not use generative AI at all in making the content of this pull
  request.
• I did use generative AI in some form in making the content of this
  pull request. I have described my use of AI below.

I used AI to help with styling on frontend to resemble the figma prototype closely (mostly from figma dev mode but used AI to refine the graph components). Also used AI to refactor the code into reusable components and pages.

Contributor Checklist

• I have manually reviewed all content submitted to gittuf in this pull
  request.
• I fully understand the content I am submitting.
• The changes introduced are documented and have tests included if
  applicable.
• My changes do not infringe on copyright/trademarks/etc.
• All commits in this pull request include a DCO
  Signoff.
• By submitting this pull request, I agree to follow the gittuf Code of
  Conduct.