ci: add GitHub Actions workflow

Author: chripiermarini

.github/workflows/ci.yml

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+name: CI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+jobs:
+  test-and-format:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+
+      - name: Install dependencies
+        run: |
+          pip install -e ".[dev]"
+          pip install -r requirements.txt
+
+      - name: Check formatting
+        run: |
+          python -m black --check src/ tests/ scripts/
+
+      - name: Run tests
+        run: |
+          python -m pytest tests/ -v

HOW-TO-CONTRIBUTE.md

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+# Contributing to Decision Intelligence Logistics Engine
+
+Thank you for your interest in contributing. This document covers everything you need to get started: setting up your environment, running tests, formatting code, and submitting a pull request.
+
+---
+
+## Table of Contents
+
+1. [Prerequisites](#prerequisites)
+2. [Fork and Clone](#fork-and-clone)
+3. [Environment Setup](#environment-setup)
+4. [Project Structure](#project-structure)
+5. [Running Tests](#running-tests)
+6. [Code Formatting](#code-formatting)
+7. [Branching and Commits](#branching-and-commits)
+8. [Opening a Pull Request](#opening-a-pull-request)
+9. [Reporting Issues](#reporting-issues)
+
+---
+
+## Prerequisites
+
+- Python **3.11 or higher**
+- `git`
+- A virtual environment tool (`venv` is fine)
+
+---
+
+## Fork and Clone
+
+1. Fork the repository on GitHub.
+2. Clone your fork locally:
+
+```bash
+git clone https://github.com/<your-username>/decision-intelligence-logistics-engine.git
+cd decision-intelligence-logistics-engine
+```
+
+3. Add the upstream remote so you can stay in sync:
+
+```bash
+git remote add upstream https://github.com/chripiermarini/decision-intelligence-logistics-engine.git
+```
+
+---
+
+## Environment Setup
+
+Create and activate a virtual environment, then install all dependencies (core + dev):
+
+```bash
+python -m venv .venv
+source .venv/bin/activate        # Windows: .venv\Scripts\activate
+
+pip install -e ".[dev]"
+pip install -r requirements.txt
+```
+
+The `.[dev]` extras install `pytest`, `hypothesis`, and `black`. The `requirements.txt` adds the API dependencies (`fastapi`, `uvicorn`) and any other runtime packages.
+
+---
+
+## Project Structure
+
+```
+src/
+  api/            # FastAPI app and LogisticsAPI facade
+  forecasting/    # Per-destination forecasting pipeline and models
+  optimization/   # LP formulation and OR-Tools solver
+  simulation/     # Stochastic scenario generation
+  utils/          # Shared helpers
+tests/
+  forecaster/     # Unit tests for individual forecasters
+  forecasting/    # Integration tests for the forecasting pipeline
+  optimization/   # Tests for the optimization module
+  utils/          # Tests for shared utilities
+scripts/          # Runnable end-to-end examples
+configs/          # YAML configuration files
+```
+
+---
+
+## Running Tests
+
+All tests live under `tests/` and are run with `pytest`. The project uses both standard unit tests and property-based tests via `hypothesis`.
+
+**Run the full suite:**
+
+```bash
+python -m pytest tests/ -v
+```
+
+Or via the Makefile shortcut:
+
+```bash
+make test
+```
+
+**Run a specific module:**
+
+```bash
+python -m pytest tests/optimization/ -v
+```
+
+**What to check before opening a PR:**
+
+- All existing tests pass.
+- New behaviour is covered by at least one test.
+- Property-based tests (if any) are not flaky — run them a couple of times if unsure.
+
+---
+
+## Code Formatting
+
+This project uses [Black](https://black.readthedocs.io/) with a line length of **88** and a target of Python 3.11 (configured in `pyproject.toml`).
+
+**Format all source files before committing:**
+
+```bash
+python -m black src/ tests/ scripts/
+```
+
+Or via the Makefile:
+
+```bash
+make format
+```
+
+**Check formatting without modifying files** (useful in CI or for a quick pre-commit sanity check):
+
+```bash
+python -m black --check src/ tests/ scripts/
+```
+
+Or:
+
+```bash
+make lint
+```
+
+> Pull requests that fail the `black --check` step will be asked to reformat before merging. Running `make format` locally is the easiest way to avoid this.
+
+---
+
+## Branching and Commits
+
+**Branch naming:**
+
+| Type | Pattern | Example |
+|---|---|---|
+| Feature | `feat/<short-description>` | `feat/add-exponential-smoothing` |
+| Bug fix | `fix/<short-description>` | `fix/optimizer-infeasible-edge-case` |
+| Refactor | `refactor/<short-description>` | `refactor/decouple-optimize-from-forecast-config` |
+| Docs | `docs/<short-description>` | `docs/update-api-readme` |
+| Tests | `test/<short-description>` | `test/hypothesis-coverage-forecaster` |
+
+**Commits:**
+
+- Use the [Conventional Commits](https://www.conventionalcommits.org/) style: `type(scope): short description`.
+- Keep commits focused — one logical change per commit.
+- Write the subject line in the imperative mood: *"add exponential smoothing"*, not *"added"* or *"adding"*.
+
+Examples:
+
+```
+feat(forecasting): add exponential smoothing model
+fix(optimization): handle infeasible LP when demand exceeds capacity
+refactor(api): make PerDestinationConfig optional for optimize-only usage
+test(forecasting): add hypothesis tests for pipeline edge cases
+```
+
+---
+
+## Opening a Pull Request
+
+1. Push your branch to your fork:
+
+```bash
+git push origin feat/your-feature
+```
+
+2. Open a PR against `chripiermarini:main` on GitHub.
+
+3. In the PR description, include:
+   - What problem it solves (reference the issue with `Closes #N` if applicable).
+   - A brief summary of the approach.
+   - Any trade-offs or alternatives you considered.
+
+4. Before requesting review, confirm locally:
+
+```bash
+make format   # or: python -m black src/ tests/ scripts/
+make lint     # should report "All done! ✨"
+make test     # all tests must pass
+```
+
+Pull requests are automatically checked through GitHub Actions. 
+PRs must pass all formatting and test checks before they can be merged.
+---
+
+## Reporting Issues
+
+Open a GitHub Issue and include:
+
+- A short, descriptive title.
+- Steps to reproduce (for bugs) or a clear description of the desired behaviour (for features).
+- Any relevant tracebacks, logs, or code snippets.
+- Your Python version (`python --version`) and OS.
+
+For questions or discussion, prefer opening an Issue over a direct message so the conversation stays visible to all contributors.