Add issue templates, contribution guidelines, and code of conduct; update CI/CD workflows and project metadata

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

CONTRIBUTING.md

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+# Contributing
+
+Thanks for taking the time to contribute — you’re helping make the Dart ecosystem better.
+
+By participating in this project, you agree to follow our [Code of Conduct](CODE_OF_CONDUCT.md).
+
+## Ways to contribute
+
+- Report bugs
+- Suggest enhancements
+- Improve documentation
+- Submit pull requests
+- Share examples and use-cases
+
+## Questions and discussions
+
+If you’re unsure whether something is a bug or a feature request, open an issue and describe:
+
+- What you expected to happen
+- What actually happened
+- Steps to reproduce (if applicable)
+- Your Dart SDK version (`dart --version`)
+
+## Filing issues
+
+When opening an issue, please include:
+
+- A clear title and description
+- Reproduction steps (minimal, if possible)
+- Expected vs actual behavior
+- Logs, stack traces, or screenshots (if relevant)
+
+## Development setup
+
+Prerequisites:
+
+- Dart SDK (see `pubspec.yaml` for the supported SDK range)
+
+Common commands:
+
+- Get dependencies: `dart pub get`
+- Format: `dart format .`
+- Analyze: `dart analyze`
+- Run tests: `dart test`
+
+Tip: Keep your editor set to “format on save”.
+
+## Pull requests
+
+We welcome PRs of all sizes. Small, focused PRs are easiest to review.
+
+### Before you submit
+
+- Run `dart format .`
+- Run `dart analyze`
+- Run `dart test`
+- Update documentation if behavior or APIs changed
+- Add or update tests for bug fixes and new features
+- If you changed public API, update `CHANGELOG.md`
+
+### PR scope guidelines
+
+- Keep PRs focused on a single concern (feature, fix, docs)
+- Avoid drive-by refactors unless they’re necessary for the change
+- Prefer backwards-compatible improvements when possible
+
+### Review process
+
+Maintainers will aim to respond, but response time can vary. If you haven’t heard back after a reasonable amount of time, a gentle ping is welcome.
+
+## Security
+
+If you discover a security issue, please **do not** open a public issue.
+
+Instead, report it privately to the maintainer(s)!
+
+## Licensing of contributions
+
+Unless stated otherwise, contributions you submit are provided under this project’s license (see [LICENSE](LICENSE)).
+
+If your organization requires a Contributor License Agreement (CLA) or similar, replace this section with your preferred process.