Write a developer onboarding guide

Write a comprehensive developer onboarding guide for [Project]. Structure it to cover: how to clone the repository and configure local tooling including required tool versions and installation instructions, how to populate all required environment variables using the .env.example as a reference, how to run the application locally and inside Docker, how to run the full test suite and interpret the output, a high-level architecture overview with a description of the key components and how they interact, and links to team resources such as the internal wiki, runbooks, and communication channels.