Add Nexus Platform phase 0 foundation scaffold

[rgomids]

Summary

• bootstrap the NestJS application with TypeScript strict mode and a GET /health endpoint
• add centralized environment config, structured pino logging, OpenTelemetry bootstrap, and PostgreSQL connectivity with pg
• create the modular monolith folder structure and placeholder modules for identity, organizations, users, access control, and audit logs
• add Docker, Compose, Makefile, CI workflow, and baseline project documentation including phase status, commands, architecture, changelog, and ADRs

Testing

• npm run lint
• npm run build
• npm run test:ci
• integration and functional suites are implemented with Testcontainers and skip when Docker is unavailable locally