Phase 5: Add tests, documentation, and production deployment

Summary:
Testing:

• Add Jest backend tests (19 tests: service/incident controllers, auth middleware)
• Add Vitest frontend tests (38 tests: status utils, StatusBadge, OverallStatus, ServiceGroup)

Documentation:

• Rewrite root README with full API reference, env vars, and deployment guide
• Rewrite backend/frontend READMEs with current structure and dev guides
• Add docs/architecture.md with Mermaid diagrams (system overview, component tree, backend MVC, database ER, status flow, incident lifecycle)

Deployment:

• Add production Dockerfiles (backend: non-root user, frontend: multi-stage Nginx)
• Add docker-compose.prod.yml override
• Add frontend nginx.conf with SPA routing and gzip
• Update .env.example with SMTP notification vars

Reviewers: ieli

Reviewed By: ieli

Differential Revision: https://devcentral.nasqueron.org/D3966