Delete Async Chat Stream

Delete an asynchronous chat stream and clean up all associated resources. This endpoint permanently removes a chat stream from storage and cleans up all associated resources including: * Stream metadata and status information * Cached events and message content * Task references and cancellation tokens Notes: * Stream must exist to be deleted (returns 404 otherwise) * Active streams are automatically cancelled before deletion * No response body returned on successful deletion (204 status) * Use status endpoint to verify deletion if needed