Set up project scaffolding: GitHub Actions workflows, issue templates, changelog, contributing guidelines, MIT license, and README

CONTRIBUTING.md

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+# Contributing
+
+Contributions are welcome.
+
+## Process
+
+1. Fork the repo and create a branch (e.g. `feature/xyz` or `fix/abc`).
+2. Make your changes and test locally:
+   ```bash
+   ./gradlew build
+   ```
+3. Open a pull request against `main`/`master` (fill in the PR template).
+4. CI must pass; address review feedback as needed.
+
+## Code
+
+- Java 21; follow the existing code style.
+- Prefer adding tests in `src/test/` for new functionality.
+
+## Questions
+
+For questions and general discussion: [Discussions](https://github.com/jakubbbdev/terminal-ui/discussions).