Migrate CI to Github Actions

[zetter-rpf]

Status

• Closes Migrate CI from CircleCI to Github Actions - Editor-API #219
• Related to https://github.com/RaspberryPiFoundation/digital-editor-issues/issues/1144
• Related to https://github.com/RaspberryPiFoundation/digital-engineering/issues/44

What's changed?

Replace our Circle CI integration with Github actions.

My motivation for doing this now was a flakey test in https://github.com/RaspberryPiFoundation/digital-editor-issues/issues/1144

It's possible that the different test environment may reduce flakyness.

Steps to perform after deploying to production

• Update shared spreadsheet/issue in https://github.com/RaspberryPiFoundation/digital-engineering/issues/44
• Change main branch settings to remove required CircleCI code coverage check and add github action test & lint checks (some of this might need to be done before merging)

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[github-actions]

Test coverage

89.07% line coverage reported by SimpleCov.
Run: https://github.com/RaspberryPiFoundation/editor-api/actions/runs/22494466969

[Copilot]

Pull request overview

This pull request migrates the CI/CD infrastructure from CircleCI to GitHub Actions. The change is motivated by organizational shift away from CircleCI and a desire to potentially reduce test flakiness through a different test environment. The migration is comprehensive, removing all CircleCI artifacts and replacing them with equivalent GitHub Actions workflows.

Changes:

• Replaced CircleCI configuration with a GitHub Actions workflow that runs linting and tests
• Implemented custom bash scripts for test coverage reporting via PR comments
• Updated development environment configuration by removing CircleCI-specific extensions
• Updated documentation to reflect the new CI platform

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
AGENTS.md	Updated CI documentation to reference GitHub Actions with Ruby 3.4, Postgres 12, Redis
.github/workflows/ci.yml	New CI workflow with lint and test jobs, including postgres and redis services, coverage reporting
.github/scripts/post_coverage_comment.sh	New script to post or update coverage comments on PRs using GitHub API
.github/scripts/build_coverage_comment.sh	New script to parse SimpleCov coverage data and format it for PR comments
.devcontainer/devcontainer.json	Removed CircleCI VSCode extension from development container
.circleci/record_coverage	Deleted legacy CircleCI coverage recording script
.circleci/config.yml	Deleted legacy CircleCI configuration file

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[adrian-rpf]

Looks good.
Just the question on if you think the EDITOR_ENCRYPTION_KEY should be excluded.