Set up comprehensive GitHub Actions CI/CD pipeline

[Copilot]

This PR implements a complete GitHub Actions test runner and CI/CD pipeline for the Tango Elixir OAuth library, addressing the requirements outlined in the README.md and Elixir configuration files.

🚀 What's Added

Core CI Pipeline (.github/workflows/ci.yml)

• PostgreSQL Service: Configured with postgres:postgres credentials matching config/test.exs
• Elixir Environment: Uses Elixir 1.15.7 with OTP 26.1 as specified in mix.exs
• Test Execution: Leverages the project's custom test alias that runs ecto.create, ecto.migrate, then test
• Coverage Reporting: GitHub integration using ExCoveralls with 85% minimum requirement
• Code Quality: Format checking and Credo static analysis using the existing mix quality alias
• Dependency Caching: Optimized for faster CI runs

Additional Workflows

• Release Automation (.github/workflows/release.yml): Tag-triggered releases with documentation generation and optional Hex.pm publishing
• Security Scanning (.github/workflows/security.yml): Trivy vulnerability scanning with weekly scheduled runs
• Matrix Testing (.github/workflows/matrix.yml): Multi-version compatibility testing across Elixir 1.15.0-1.16.0 and OTP 26.0-26.2

Configuration Updates

• Enhanced mix.exs: Added coveralls.github to preferred CLI coverages for GitHub integration
• Comprehensive Documentation: Created .github/README.md with setup instructions, troubleshooting, and usage examples

🔧 Key Features

The implementation carefully follows the project's existing setup:

• Uses the exact database configuration from config/test.exs
• Respects the Elixir version constraints in mix.exs
• Leverages existing Mix aliases for consistent behavior
• Handles all test dependencies including bypass for HTTP testing
• Maintains the 85% coverage requirement from .coveralls.exs

The workflows will automatically run on push/PR to main or develop branches, providing immediate feedback on code quality, test results, and security vulnerabilities.

Fixes #1.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https (dns block)
• repo.hex.pm
  • Triggering command: /usr/lib/erlang/erts-13.2.2.5/bin/inet_gethost 4 (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

---

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[Copilot]

@cpursley 👋 This repository doesn't have Copilot instructions. With Copilot instructions, I can understand the repository better, work faster and produce higher quality PRs.

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[github-advanced-security]

This pull request sets up GitHub code scanning for this repository. Once the scans have completed and the checks have passed, the analysis results for this pull request branch will appear on this overview. Once you merge this pull request, the 'Security' tab will show more code scanning analysis results (for example, for the default branch). Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results. For more information about GitHub code scanning, check out the documentation.

[cpursley]

@copilot this came up in test runner but mix format run locally worked fine!:

Run mix format --check-formatted
  mix format --check-formatted
  shell: /usr/bin/bash -e {0}
  env:
    MIX_ENV: test
    GITHUB_TOKEN: ***
    INSTALL_DIR_FOR_OTP: /home/runner/work/_temp/.setup-beam/otp
    INSTALL_DIR_FOR_ELIXIR: /home/runner/work/_temp/.setup-beam/elixir
** (Mix) mix format failed due to --check-formatted.
The following files are not formatted:

/home/runner/work/tango/tango/mix.exs

       |
12 12  |      aliases: aliases(),
13 13  |      test_coverage: [tool: ExCoveralls],
14    -|      preferred_cli_coverages: ["coveralls", "coveralls.detail", "coveralls.html", "coveralls.github"],
   14 +|      preferred_cli_coverages: [
   15 +|        "coveralls",
   16 +|        "coveralls.detail",
   17 +|        "coveralls.html",
   18 +|        "coveralls.github"
   19 +|      ],
15 20  |      dialyzer: [
16 21  |        plt_file: {:no_warn, "priv/plts/dialyzer.plt"}
       |



Error: Process completed with exit code 1.