bindPersona method
Bind a persona without installing a local model.
Cloud chat only needs a persona + a configured SyniCloudConfig;
it doesn't run the on-device engine. Hosts that pick
SyniExecutionMode.cloudOnly can call this once instead of
downloading a model just to bind a persona. Local / localFirst
modes still require install to have completed (it loads the
engine), and install continues to bind the persona itself.
Idempotent — re-binding the same persona is harmless. Replacing the persona while a model is installed is allowed; the persona you bind last is the one chat methods use.
Implementation
void bindPersona(SyniPersona persona) {
_persona = persona;
}