Function grant_access 

pub async fn grant_access(
    pool: &SqlitePool,
    did: &str,
    handle: Option<&str>,
    granted_by: &str,
    invite_code_used: Option<&str>,
) -> Result<()>

Grant a beta seat directly (admin / seed path — no code consumed). Idempotent on did (re-granting updates the row rather than erroring).