docs: add CONTRIBUTING.md and SECURITY.md for open source

CONTRIBUTING.md

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+# Contributing to Linux-Patch-Api
+
+Thank you for your interest in contributing to Linux-Patch-Api! We appreciate every contribution — from bug reports and documentation improvements to new features and security fixes.
+
+## Code of Conduct
+
+This project follows the [Contributor Covenant v2.1](https://www.contributor-covenant.org/version/2/1/code_of_conduct/) code of conduct. By participating, you are expected to uphold this standard. Please report unacceptable behavior to the maintainers.
+
+## How to Contribute
+
+1. **Fork** the repository
+2. Create a **feature branch** from `main`:
+   ```bash
+   git checkout -b feat/my-feature
+   ```
+3. Make your changes
+4. Ensure all CI checks pass:
+   ```bash
+   cargo fmt --check
+   cargo clippy -- -D warnings
+   cargo test
+   ```
+5. **Commit** using conventional commit format (see below)
+6. Open a **Pull Request** against `main`
+
+## Development Setup
+
+### Prerequisites
+
+- **Rust toolchain** (stable) — [rustup](https://rustup.rs/)
+- **System dependencies**:
+  ```bash
+  sudo apt-get install build-essential libsystemd-dev pkg-config libssl-dev
+  ```
+
+### Build & Run
+
+```bash
+cargo build
+cargo test
+```
+
+## Commit Messages
+
+We use [Conventional Commits](https://www.conventionalcommits.org/):
+
+| Prefix   | Usage                  |
+|----------|------------------------|
+| `feat:`  | New feature            |
+| `fix:`   | Bug fix                |
+| `docs:`  | Documentation changes  |
+| `chore:` | Maintenance tasks      |
+| `refactor:` | Code refactoring    |
+| `test:`  | Adding or updating tests |
+| `ci:`    | CI configuration changes |
+
+Example:
+```
+feat: add endpoint for patch rollback
+```
+
+## Pull Request Requirements
+
+- All CI checks must pass (fmt, clippy, test, audit, build)
+- One feature or fix per PR — keep changes focused
+- Include a clear description of what changed and why
+- Update documentation if your change affects behavior
+
+## Reporting Issues
+
+Use [GitHub Issues](https://github.com/Draco-Lunaris/Linux-Patch-Api/issues) to report bugs, request features, or ask questions. Please include:
+
+- Steps to reproduce (for bugs)
+- Expected vs. actual behavior
+- Relevant logs or error messages
+
+## License
+
+By contributing, you agree that your contributions are licensed under the [Apache License 2.0](LICENSE), the same license as this project.