## Why

SentryAgent.ai AgentIdP Phase 1 MVP is complete and `docs/developers/` covers API consumers. However, there is no documentation for the engineers who deploy, configure, and operate the infrastructure. A DevOps engineer joining the project today has no reference for environment variables, database schema, deployment procedure, security configuration, or operational runbook. We fix that now.

## What Changes

- New `docs/devops/` folder — fully separate from `docs/developers/` — containing a complete operational reference for DevOps engineers
- System architecture overview: components, ports, dependencies, data flow
- Complete environment variable reference: every variable, required vs optional, format, examples
- Database documentation: 4-table schema, migration runner, how to apply/verify migrations
- Local development guide: docker-compose infrastructure setup, service ports, health checks
- Security guide: RSA keypair generation and rotation, CORS config, secret storage
- Operations runbook: startup procedure, graceful shutdown (SIGTERM/SIGINT), logging, common failures and fixes

## What Does Not Change

- `docs/developers/` — not touched
- Source code — documentation only
- No new dependencies