Fix create_remotes on GitHub and make the API tests configurable

[hannahlanzrath]

Bug fixes

• create_remotes on GitHub: it read ssh_url_to_repo from the created repositories, an attribute only GitLab projects have. On GitHub it created both repositories and then failed with an AttributeError, so repo.create_remotes(...) / rdm remote create never worked there. Each remote class now has ssh_url(response), which returns the SSH URL for its host.
• GitLabRemote.delete_remote: its name and namespace checks ended in pass instead of continue, so it deleted every project the search returned. It now only deletes the exact project namespace/name.

Configurable API tests (tests/test_gitlab_api.py → tests/test_remote_api.py)

• Accounts: the server_api tests were hardcoded to one developer's accounts and used a fixed repository name. They now read their accounts from environment variables:
  • CADET_RDM_TEST_GITLAB_NAMESPACE, CADET_RDM_TEST_GITHUB_NAMESPACE
  • optional: CADET_RDM_TEST_GITLAB_URL, CADET_RDM_TEST_GITLAB_USERNAME, CADET_RDM_TEST_GITHUB_USERNAME
• Skipping: tests for a host without a namespace are skipped with a message saying which variable to set.
• No collisions: every run uses random repository names and deletes them in a finally block, so runs by different developers can't interfere.
• Coverage: the tests now run against GitHub and GitLab alike; before, only GitLab had an integration test, which is why the GitHub bug went unnoticed.
• Docs: CONTRIBUTING.md describes the variables, tokens and SSH requirements, and the release checklist template points there.

Offline tests (tests/test_remote_integration.py, run in CI)

• create_remotes adds the right SSH URLs for faked GitHub and GitLab responses.
• delete_remote deletes only the exact match.
• Both tests fail on the old code.

The CI test selection passes locally (76 passed).

Run against GitHub: with CADET_RDM_TEST_GITHUB_NAMESPACE=hannahlanzrath, both GitHub tests pass. That includes create_remotes, which confirms the fix against the real API, and no test repositories were left behind. The GitLab tests were skipped because no GitLab token was available.

Cleanup safety: the tests only delete repositories they created themselves (recorded after a successful create_remote), and they warn about any repository they couldn't delete.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.33333% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cadetrdm/repositories.py	50.00%	2 Missing ⚠️
cadetrdm/remote_integration.py	92.85%	1 Missing ⚠️

Files with missing lines	Coverage Δ
cadetrdm/remote_integration.py	46.15% <92.85%> (+18.99%)	⬆️
cadetrdm/repositories.py	61.64% <50.00%> (+0.95%)	⬆️

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