Update startSseConsumer JSDoc to reflect new priority semantics
The SDK `startSseConsumer` and `useStartSseConsumer` JSDocs still
described the old "pass a URL as a fallback for instances without
stored config" behavior — priority-3 semantics that no longer exist.
Under the collapsed chain, a caller-supplied URL is promoted to the
runtime override (priority 1) and wins over PDS accountConfig.
Documentation updated to match.