Support GitHub Enterprise API URLs

[gokul-debugger]

Problem

The GitHub client supports a configurable API base URL internally, but the CLI and service do not expose it. Users of GitHub Enterprise Server therefore cannot point ContribCheck at their organization instance without writing Python code. The reference parser is also hard-coded to github.com, so even a configured base URL would not accept enterprise issue URLs.

Proposed change

Expose the API endpoint through a CLI option and environment variable, and make issue-reference parsing accept any host.

contribcheck inspect owner/repository#123 --base-url https://github.example.com/api/v3

Acceptance criteria

• --base-url is supported by the inspect command.
• GITHUB_API_URL configures the CLI and FastAPI service when the option is absent.
• Precedence is documented as CLI option, environment variable, then https://api.github.com.
• URLs are validated as HTTP or HTTPS origins and trailing slashes are handled consistently.
• parse_issue_reference in src/contribcheck/parsing.py accepts issue URLs on any host (currently it rejects every host except github.com/www.github.com), while still requiring the /owner/repository/issues/N path shape.
• Authentication headers are sent only to the configured API client.
• Existing github.com behavior remains unchanged.
• Mock-transport tests cover default, environment, explicit-option, malformed URL, and non-github.com host behavior.
• The README documents GitHub Enterprise usage and token expectations.

Security note

Tests and examples must use placeholder hosts and tokens. Do not include credentials or private organization URLs.

[viftode4]

@gokul-debugger I can deliver the GitHub Enterprise URL support in this issue as a fixed 85 USDC milestone.

Scope: expose --base-url on inspect; support GITHUB_API_URL in the CLI and FastAPI service with documented CLI → environment → public-default precedence; validate and normalize HTTP(S) origins; generalize parse_issue_reference to any host while preserving the required issue path; ensure auth headers stay scoped to the configured client; add mock-transport coverage for default/env/explicit/malformed/custom-host cases; and document Enterprise usage with placeholder-only hosts/tokens.

Acceptance: every checklist item in the issue passes, existing github.com behavior remains unchanged, and the repository’s test/lint commands pass. Scope excludes access to any real private Enterprise instance, credential handling, or deployment.

If that scope and price fit, please confirm the funded milestone here before implementation. Payment can be Base USDC to the existing project receive address; no new account or credential sharing is required.

[gokul-debugger]

Thanks for the detailed offer. ContribCheck is an open-source personal project, and I am not offering paid bounties at this time. You are welcome to contribute through the normal open-source workflow, but please do not begin work with the expectation of payment.