Journey Durable

This handles the stateful actor layer by wrapping the durable-objects skill and calling manage_durable_objects to deploy per-key Durable Object classes like chat rooms, multiplayer state, or rate limiters. It reads the Durable section from your 02-plan.md, confirms each deployment with you, verifies it worked, and logs everything to 04-build-log.md. Gets skipped entirely if your plan doesn't need stateful actors. The orchestrator invokes this when current_stage hits durable, or you can call it directly if you're working through the journey manually. Straightforward glue code that keeps the multi-stage build moving forward.