docs: add CONTRIBUTING.md with three core sections

CONTRIBUTING.md

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+# Contributing to ProofWorks
+
+Thank you for considering contributing to ProofWorks! This document explains how to set up your environment, run tests, and submit a pull request.
+
+## Setup
+
+### Prerequisites
+
+- **Node.js** v18 or later
+- **Python** 3.10 or later
+- **npm** (comes with Node.js)
+
+### Installation
+
+1. Fork and clone the repository:
+   ```
+   git clone https://github.com/YOUR_USERNAME/proofworks-genlayer.git
+   cd proofworks-genlayer
+   ```
+2. Install JavaScript dependencies: `npm install`
+3. Install Python dependencies: `pip install -r requirements.txt`
+4. Copy the environment file: `cp .env.example .env`
+
+## Running the tests
+
+Run the full test suite with:
+```
+make test
+```
+
+Run individual test files:
+```
+python -m pytest tests/test_file.py -v
+```
+
+For frontend tests:
+```
+npm test
+```
+
+## Submitting a pull request
+
+1. Create a feature branch: `git checkout -b feat/your-feature`
+2. Make your changes and commit: `git add . && git commit -m "type: description"`
+3. Push: `git push origin feat/your-feature`
+4. Open a PR against the `main` branch
+5. Include a summary of changes, related issue number, and testing performed
+6. Respond to review feedback