ci: add GitHub Actions workflow

[t0kubetsu]

What

Adds .github/workflows/ci.yml — lint + tests on push and PR to main, across Python 3.11, 3.12 and 3.13.

Why

This repository had no CI. Nothing verified that a change compiled, linted, or passed its tests before reaching main — the recent Dependabot batch on mailvalidator merged against checks=0, where a green "mergeable" only ever meant "no merge conflict".

Hardening

Applied per GitHub's published guidance, matching the standard already set by testing-platform-backend:

Measure	Why
Actions pinned to full commit SHAs	A tag is mutable; @v4 can be repointed at new code
permissions: contents: read	The default GITHUB_TOKEN grant is far wider than this needs
persist-credentials: false	Otherwise a usable token stays in .git/config for later steps
concurrency + cancel-in-progress	A new push supersedes the previous run
fail-fast: false	One failing interpreter must not mask the others
timeout-minutes	A hung job cannot hold a runner indefinitely

No workflow interpolates github.event.* or github.head_ref into a run: block, so there is no script-injection surface.

Verified locally

ruff clean and the full suite green before opening this PR — CI should be green on merge.

Summary by CodeRabbit

• New Features

  • Added automated continuous integration checks for code quality and tests across Python 3.11–3.13.
  • Added Ruff linting with a defined set of project rules.

• Documentation

  • Updated project conventions to document the continuous integration workflow.

• Chores

  • Added Ruff to the development tooling.
  • Configured reliable, cached, and read-only CI runs with automatic cancellation of superseded checks.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: b4825500-5d65-42e3-985b-322fc07a0aaa

📥 Commits

Reviewing files that changed from the base of the PR and between e2e8a5d and cc67214.

📒 Files selected for processing (1)

• pyproject.toml

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📝 Walkthrough

Walkthrough

The project adds GitHub Actions validation for Ruff and pytest across Python 3.11–3.13. It adds Ruff to development dependencies, configures selected lint rules, and documents the workflow.

Changes

CI and linting

Layer / File(s)	Summary
Ruff development configuration pyproject.toml	The dev extra now includes Ruff. Ruff targets Python 3.11 and enables E4, E7, E9, and F rules.
GitHub Actions validation workflow .github/workflows/ci.yml, CLAUDE.md	GitHub Actions runs Ruff and pytest on pushes and pull requests to main across Python 3.11–3.13. The workflow uses caching, read-only permissions, cancellation of superseded runs, and a 15-minute timeout. Project documentation describes the workflow.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: afrittellalhc, nicky-mezzina-lhc

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding a GitHub Actions CI workflow.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ci/add-github-actions-workflow

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_{Comment @coderabbitai help to get the list of available commands.}

[greptile-apps]

Greptile Summary

Adds a hardened GitHub Actions workflow that runs linting and tests across Python 3.11–3.13.

• Installs Ruff through the project’s development extras and defines a stable lint configuration.
• Documents the new CI workflow in the repository guide.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
.github/workflows/ci.yml	Adds a least-privilege, SHA-pinned CI matrix that installs development dependencies before running Ruff and pytest.
pyproject.toml	Adds Ruff to development dependencies and explicitly configures its Python target and lint rules.
CLAUDE.md	Updates repository conventions to document the newly added CI workflow.

_{Reviews (5): Last reviewed commit: "ci: pin ruff to a tested major" | Re-trigger Greptile}

The merge-base changed after approval.

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@pyproject.toml`:
- Around line 62-72: Update the dev dependency declaration to pin Ruff to the
tested version instead of allowing any future release through ruff>=0.6; keep
the existing [tool.ruff] configuration and selected rule set unchanged.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 214cbedb-99b1-478b-92eb-308a06be51f5

📥 Commits

Reviewing files that changed from the base of the PR and between 5f18e4d and e2e8a5d.

📒 Files selected for processing (3)

• .github/workflows/ci.yml
• CLAUDE.md
• pyproject.toml