feat: wire Infisical secret store into API server and MCP tools

- Wire secretsManager in NewHandler() — instantiate InfisicalBackend
  when OIKOS_INFISICAL_SITE_URL is set (previously always nil)
- Add get_secret, list_secrets, set_secret MCP tools with nil-backend
  graceful degradation
- Add oikos secret get|set|list CLI subcommands for Infisical
- Fix Set() bug: create-before-update so new keys are created;
  add Type: "shared" to Update so it finds the right secret;
  disable SDK cache so Get returns fresh data after Set
- Clean enrollment response: remove fake infisical_client_id/
  infisical_client_secret stubs, store age key in Infisical for real

docker-compose.yml

@@ -76,6 +76,12 @@ services:
       OIKOS_OIDC_CLIENT_ID: ${OIKOS_OIDC_CLIENT_ID:-otkHBSueHJsYtOHstL6rn5izeGgyOsavp1qA1hod}
       OIKOS_NOMOS_AGENT_SLUG: ${OIKOS_NOMOS_AGENT_SLUG:-agent:nomos}
       NOMOS_PROXY_URL: http://nomos:8092
+      # Infisical secret store (Phase 5)
+      OIKOS_INFISICAL_SITE_URL: ${OIKOS_INFISICAL_SITE_URL:-}
+      OIKOS_INFISICAL_CLIENT_ID: ${OIKOS_INFISICAL_CLIENT_ID:-}
+      OIKOS_INFISICAL_CLIENT_SECRET: ${OIKOS_INFISICAL_CLIENT_SECRET:-}
+      OIKOS_INFISICAL_PROJECT_ID: ${OIKOS_INFISICAL_PROJECT_ID:-}
+      OIKOS_INFISICAL_ENV: ${OIKOS_INFISICAL_ENV:-dev}
     volumes:
       - ${OIKOS_SSH_KEY_PATH:-~/.ssh/id_ed25519}:/etc/oikos/ssh_key:ro
     ports: