feat: add stratum-orchestrator with graph, state, NATS, and Nickel action nodes
New crates: stratum-orchestrator (Cedar authz, Vault secrets, Nu/agent executors,
saga runner), stratum-graph (petgraph DAG + SurrealDB repo), stratum-state
(SurrealDB tracker), platform-nats (NKey auth client), ncl-import-resolver.
Updates: stratum-embeddings (SurrealDB store + persistent cache), stratum-llm
circuit breaker. Adds Nickel action-nodes, schemas, config, Nushell scripts,
docker-compose dev stack, and ADR-003.
9095ea6d8e
