chore(release): MIT license + CONTRIBUTING/SECURITY/CODE_OF_CONDUCT + README badges (S12)

CONTRIBUTING.md

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+# Contributing to portfolio-optimiser-claude
+
+Thank you for your interest in contributing! This document provides guidelines and instructions
+for contributing.
+
+## Code of Conduct
+
+Please read and follow our [Code of Conduct](CODE_OF_CONDUCT.md).
+
+## How to Contribute
+
+### Reporting Issues
+
+- Check existing issues before creating a new one
+- Provide clear reproduction steps
+- Include relevant environment details (OS, Python version)
+
+### Submitting Changes
+
+1. Fork the repository
+2. Create a feature branch (`git checkout -b feature/amazing-feature`)
+3. Make your changes following the conventions below
+4. Run the test, lint, and type checks (see Development Setup) and ensure they pass
+5. Commit your changes using [Conventional Commits](https://www.conventionalcommits.org/)
+   (`type(scope): description`)
+6. Push to your branch and open a Pull Request
+
+### Pull Request Guidelines
+
+- Follow the existing code style (`ruff` enforced)
+- Type hints everywhere; `mypy`-clean where possible
+- Include tests for new functionality — this project uses **load-bearing tests**: a test that
+  covers a seam must fail when that seam is detached, not merely pass while wired
+- The **deterministic validator is mandatory and blocking** — never make it an optional plugin
+- Keep PRs focused on a single change
+- Update documentation as needed
+
+## Development Setup
+
+Requires Python ≥ 3.10 and [`uv`](https://docs.astral.sh/uv/).
+
+```bash
+# Clone your fork
+git clone https://git.fromaitochitta.com/open/portfolio-optimiser-claude.git
+cd portfolio-optimiser-claude
+
+# Install dependencies
+uv sync
+
+# Run tests (offline, no API key required)
+uv run pytest
+
+# Lint and format
+uv run ruff check .
+uv run ruff format --check .
+
+# Type-check (strict)
+uv run mypy src
+```
+
+Tests run offline without an API key; live runs use the Claude API — keep `ANTHROPIC_API_KEY` in
+your environment, never commit it.
+
+## Questions?
+
+Feel free to open an issue for any questions about contributing.