Bug: Resource.Create was POSTing to item path (/issues/{index})
instead of collection path (/issues). Same class as the List fix.
Tests: path validation on all service methods, Update tests for
issues/repos, CreateComment test, ListComments test, PR merge
error case (conflict handling).
227 lines of test coverage added by Codex agent.
Co-Authored-By: Virgil <virgil@lethean.io>