🔀 Merge duplicate students

💡 What this does. Students sometimes spell their own name three different ways across submissions ("Marie", "marie", "Marie L."). Each spelling becomes a separate roster entry and the gradebook reports them as separate students. This page detects likely duplicates per class and lets you merge them: pick the canonical (correct) spelling, click ⇒ merge, and every Submissions row carrying the duplicate is rewritten to the canonical name.