Document app container architecture and socket proxy requirement

- TODO: add app container architecture section with socket proxy, network
  isolation, image allowlist, and Podman evaluation items
- security-auditor: hard rules for never mounting raw Docker socket and
  never spawning privileged containers

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/agents/security-auditor.md

@@ -83,3 +83,5 @@ Key management: private key (`JWT_PRIVATE_KEY`) signs tokens and must never be e
 - Never use `text()` with string interpolation in SQLAlchemy queries
 - Never expose `hashed_password`, `is_superuser`, or internal IDs in API responses unless explicitly required
 - After any code change, verify the pre-commit hook still passes
+- **Never mount `/var/run/docker.sock` directly into the backend container** — Docker socket access must always go through `tecnativa/docker-socket-proxy` on an internal-only network with a minimal API whitelist. Raw socket access inside any app container is equivalent to root on the host.
+- **Never spawn `--privileged` containers** or containers with added capabilities for app workloads