Fix test correction: remove transaction, add error handling

Replaced db.transaction() wrapper (unreliable in node:sqlite at this
version) with a plain loop. Added try/catch in the JS save handler so
any server error surfaces as a visible toast instead of failing silently.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/admin.js

@@ -2119,6 +2119,7 @@ $('#correct-test-save').addEventListener('click', async () => {
     wordId: Number(cb.dataset.wordId),
     correct: cb.checked,
   }));
+  try {
     const { score, total } = await api(`/api/tests/${correctTestId}/correct`, {
       method: 'PATCH',
       body: { corrections },
@@ -2126,6 +2127,9 @@ $('#correct-test-save').addEventListener('click', async () => {
     $('#correct-test-modal').hidden = true;
     msg(`Score updated: ${score}/${total}`);
     loadSpellingTests();
+  } catch (err) {
+    msg(err.message || 'Failed to save corrections', 'error');
+  }
 });
 
 $('#gradebook-course').addEventListener('change', () => renderGradebook($('#gradebook-course').value));

server.js

@@ -539,11 +539,9 @@ app.patch('/api/tests/:testId/correct', requirePin, (req, res) => {
   if (!test) return res.status(404).json({ error: 'Test not found' });
 
   const upd = db.prepare(`UPDATE test_answers SET correct = ? WHERE test_id = ? AND word_id = ?`);
-  db.transaction(() => {
   for (const c of corrections) {
     upd.run(c.correct ? 1 : 0, testId, c.wordId);
   }
-  })();
 
   const newScore = db.prepare(`SELECT COUNT(*) AS n FROM test_answers WHERE test_id = ? AND correct = 1`).get(testId).n;
   db.prepare(`UPDATE tests SET score = ? WHERE id = ?`).run(newScore, testId);