Function update_profile 

pub async fn update_profile(
    name: String,
    avatar: String,
    banner: String,
    about: String,
    handler: &dyn ProfileSyncHandler,
) -> bool

Update the current user’s profile metadata and broadcast to relays.

Merges the provided fields with the existing profile (empty = keep existing). After successful broadcast, updates STATE and notifies via EventEmitter + handler.