Feat/git backend 4534

[nafisa404]

Summary

Introduced Git backend integration for Music Blocks (Issue #4534).

This PR includes:

• /commit endpoint using FastAPI + GitPython
• /log endpoint to return commit history
• HTML frontend widget to commit and view project history

Files Added

• git-backend/main.py: FastAPI backend
• git-backend/requirements.txt: Backend dependencies
• activity/git-widget.html: Frontend UI

🔗 Related Issue

Fixes #4534

Mentors to Review

@walterbender @pikurasa @sum2it

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[walterbender]

I am not quite sure what I am looking at here. (I presume that the tempo commit is unrelated.) How does MB interact with your widget?

[nafisa404]

Thank you for the feedback, @walterbender!

You're right — the Tempo UI fix and AI-related commits were unintentionally included in this PR. I’ll split them into separate pull requests for clarity.

Regarding this PR (Git backend for #4534):

This introduces a FastAPI backend that accepts .json project files exported from Music Blocks.

The widget (git-widget.html) is designed as a prototype UI for interacting with the Git backend.

The intended future integration is to allow Music Blocks to:

Auto-export or trigger a download of the project state

Send it via fetch() to /commit along with a user-supplied message

Query commit history using /log to show a project timeline or fork graph

I'm happy to add a usage flow or link the exported JSON to Music Blocks directly in a follow-up PR, if that’s preferred.

I’ll clean up the commit history now and rebase this branch so this PR focuses only on the Git backend implementation for #4534.

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.