Stream workflow run events (SSE)

Scope: workflows:read. Free. Ordered at-least-once SSE for successfully persisted frames; resume with Last-Event-ID or ?after=<seq>. Workflow event appends, including terminal frames, are best-effort and can be absent if storage or the worker fails after the durable state transition. The edge may rotate a connection after 300 seconds; reconcile authoritative state with GET /v1/workflows/runs/{run_id} rather than waiting indefinitely for a terminal frame.

As with run streams, the connection can close on event: done, on event: timeout with data: {"reason":"stream_max_duration"} when the server's stream wall-clock ceiling is reached (the workflow run may still be going), or on event: error with data: {"code":..., "message":...}. Only done describes the run; the other two describe the stream.