Move to github actions / remove circleci config

Editor assessment

The header `ci: move to github actions / remove circleci config` states the changed behavior directly, so a reader grasps what was fixed and where without consulting the diff. The `ci` type is accurate and the absence of a scope is acceptable here. No body or footer is required for a change of this size. Style is clean: imperative mood, no trailing period, and a subject well within a sensible length. A body explaining the underlying cause would make this fully instructive, but for a contained change the omission is acceptable, leaving a clear, correct, publishable message.