Stream workflow history events via Server-Sent Events

Opens a persistent SSE connection that delivers Temporal workflow history events in real time. Emits named events: workflow (metadata, once), history (event batches), done (terminal state), server_error (post-flush errors). The done event carries { reason, newRunId? } where reason is the terminal Temporal event type (WORKFLOW_EXECUTION_COMPLETED, WORKFLOW_EXECUTION_FAILED, WORKFLOW_EXECUTION_TIMED_OUT, WORKFLOW_EXECUTION_CANCELED, WORKFLOW_EXECUTION_TERMINATED, WORKFLOW_EXECUTION_CONTINUED_AS_NEW) and newRunId is present only when the terminal event chains a follow-on run. server_error carries { error, message, workflowId, runId }. Errors before the stream opens are returned as JSON HTTP responses (400/404); once open, failures arrive as a server_error event. Supports reconnect via Last-Event-ID header or lastEventId query param.