Function update_image 

pub async fn update_image(
    client: &DockerClient,
    progress: &mut ProgressReporter,
) -> Result<UpdateResult, DockerError>

Update the opencode image to the latest version

This operation:

1. Tags the current image as “previous” for rollback
2. Pulls the latest image from the registry

Returns UpdateResult indicating success or if already on latest.

Arguments

• client - Docker client
• progress - Progress reporter for user feedback