Add GitHub Enterprise support to GitHubClient

[Copilot]

Fixes #2623

This PR implements GitHub Enterprise Server (GHE) support by enabling the GitHubClient to work with custom GitHub Enterprise installations that use the API endpoint pattern https://<ghe-domain>/api.

Changes Made

GitHubClient Enhancements

• Added domain tracking to store the repository's GitHub domain
• Updated setRepo() method to accept an optional domain parameter
• Modified the internal newClient() function to dynamically construct the correct API base URL based on the domain

Smart URL Construction

The client now intelligently determines the API endpoint:

• GitHub.com: Uses the standard https://api.github.com
• GitHub Enterprise: Uses https://<domain>/api pattern

Integration Updates

• Updated the GitHub class constructor to pass domain information from the repository to the GitHubClient
• Ensures the client is reset when domain information changes to pick up the new API endpoint

Example Usage

With a GitHub Enterprise installation at github.mycompany.com, the client will now automatically:

1. Detect the enterprise domain from the repository information
2. Construct the correct API URL: https://github.mycompany.com/api
3. Make API calls to the enterprise instance instead of GitHub.com

Testing

Added comprehensive test coverage including:

• Basic functionality verification for both GitHub.com and Enterprise domains
• Client reset behavior when switching between domains
• URL construction validation for various enterprise domain patterns
• Integration tests ensuring existing GitHub.com functionality remains unchanged

Backward Compatibility

This change is fully backward compatible - existing GitHub.com repositories continue to work exactly as before, with no configuration changes required.

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1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
gitbutler-web	Skipped			Sep 13, 2025 8:57am

[Byron]

This PR, particularly the tests, look good in principle, but maybe it's too much for what it actually should do.
I patched it up to maybe actually do something useful, but I think it's time for someone more experienced to take a look.
From what I can tell, the URLs are now correctly generated, but of course I wasn't able to test it for real.
I was, however, able to verify that the standard GitHub client still works.

This for some reason didn't work as it didn't find the function that should exist according to the type system, but I assume it's not really needed.

Thanks @estib-vega for taking a look 🙏.

[krlvi]

I am not sure this is how we want to approach this. Perhaps if there is a quick win here it would be great. Otherwise, I would like to move the GitHub/forge functionality more on the rust end

[Byron]

That makes sense - if the code here is salvageable I think it qualifies as quick win, but moving everything to Rust is certainly more effort. However, even that effort might be acceptable if AI can do the port - a task it's supposedly good at.