fix: enable line numbers in drill mode code editor

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: davidagustin

app/[language]/drill/page.tsx

@@ -878,7 +878,7 @@ function DrillPhaseComponent({
             language={currentProblem.sourceLanguage}
             height={120}
             minHeight={120}
-            lineNumbers={false}
+            lineNumbers={true}
             autoFocus
             onSubmitShortcut={handleSubmit}
             className="border-zinc-700"