Export flow for runtime (limited preview)

Export a fully-resolved, self-contained flow definition that the @runtypelabs/runtime package can consume directly at boot. All step configs are inlined; no live DB queries are needed at execution time. Requires the `RUNTIME:EXPORT` scope and an Enterprise plan (the `byoc` entitlement); an unentitled account receives `403` with code `BYOC_PLAN_REQUIRED` in every environment. The response carries `hostDependencies`: the runtime seams the exported artifact needs a host to wire before it can run everything it describes. A durable-class step (`wait-until` or `crawl`) anywhere in the flow's executable closure declares a `durable-pause-host` dependency; a detached-capable dynamic subagent pool or a detached inline subagent tool declares a `background-run-coordinator` dependency. The array is empty when nothing needs wiring, and the export is never refused for a declared dependency.