Added unit tests for frontend

[HarK-github]

Description

References Issue: #31
This pull request introduces the initial automated end-to-end test suite for the gittuf Security Explorer using Playwright. As these are the first E2E tests for the project, the focus is on establishing foundation for testing repository selection, commit browsing, and metadata visualization.

Key features of this initial setup:

1. Base Repository Selection Logic
   Established the core flow for connecting to repositories. The tests are designed to handle the transition from the initial landing state to a "Connected" state, ensuring the UI has successfully processed repository metadata before proceeding.
   For testing purposes, demo repository is used to generate interactions.

2. Commit Browsing and Analysis
   Created the first tests for the commit list component. These include logic to ensure the "Browse Commits" view is correctly populated and accessible, even when application defaults might trigger automatic transitions to other views.

3. Visualization Rendering Foundation
   Introduced specialized tests for the Trust Graph and JSON Tree View. These tests implement wait-logic for loading overlays and verify that the complex rendering components (Canvas and SVG) are correctly initialized in the DOM.

4. Resilient Synchronization Patterns
   Given the variable latency of Git operations, this setup implements strategic timeouts and visibility checks. By avoiding static sleeps and instead waiting for specific UI markers, the suite provides a stable framework that reduces flakiness in CI environments.

AI Usage

• 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 generative AI to help diagnose race conditions between the React state transitions and the Playwright test runner during this initial setup. The AI provided guidance on utilizing role-based locators. I manually reviewed all outputs, aligned them with Playwright best practices, and integrated the logic into the final test code to ensure a high-performance testing foundation.

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](https://wiki.linuxfoundation.org/dco).
• By submitting this pull request, I agree to follow the gittuf [Code of Conduct](https://github.com/gittuf/community/blob/main/CODE-OF-CONDUCT.md).

[HarK-github]

@patzielinski please review

[patzielinski]

Thanks for opening this, @HarK-github.

In addition to the items that I've flagged, please also check off the appropriate boxes in the pull request template (the checklist was left empty).

Once you've addressed these items, I'm going to take a second review pass. Let me know if you have questions. Thanks!

[patzielinski]

What is this line for?

[HarK-github]

This is for uploading the test reports. In this case it will upload and store tests reports regardless of whether if it fails or pass.

[patzielinski]

Yes, but why is there the if statement?

[patzielinski]

Can you add this as another job to the Frontend CI?

[patzielinski]

Bump on this?

[HarK-github]

Please check.

[HarK-github]

@patzielinski could you please review remaining code

[HarK-github]

@patzielinski I have fixed some tests and frontend ci is running the tests successfully .