docs+ci: Boost documentation and test coverage

[laurentketterle-hub]

Documentation & CI Boost

This PR adds comprehensive documentation and CI/CD workflows to improve project quality and contributor experience.

Documentation Added

• ARCHITECTURE.md: Project architecture overview, design patterns, component structure
• API.md: Complete API reference with endpoints, authentication, error codes, rate limiting
• CONTRIBUTING.md: Contributor guide with setup, workflow, commit conventions, PR process
• DEPLOYMENT.md: Deployment guide covering Docker, environments, monitoring, security

CI/CD Added

• ci.yml: Multi-version test matrix (Python/Go/Node/Rust), linting, coverage
• code-quality.yml: Code quality checks, documentation verification, dependency audit
• docker.yml: Docker image build with BuildKit caching

Impact

• Improved onboarding experience for new contributors
• Enhanced project maintainability with documented architecture
• Reliable CI pipeline for quality assurance
• Docker build validation on every PR