Function apply_status_policy 

pub fn apply_status_policy(
    task: &mut Task,
    status: TaskStatus,
    now_rfc3339: &str,
    note: Option<&str>,
) -> Result<()>

Apply the shared status-transition policy to a task.

This updates status, updated_at, and completed_at based on terminal states, and optionally appends a redacted note.