test(benchmarks): add A/B task fixtures with hidden checks

Ten small Python tasks, each failing on the fixture and passing with a
reference solution, including workflow expectations for a small change, a
bugfix, and a delegable change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/benchmarks/tasks/02-bugfix-pagination/hidden/test_hidden.py

@@ -0,0 +1,11 @@
+import unittest
+from app.pagination import paginate
+
+
+class Hidden(unittest.TestCase):
+    def test_last_page(self):
+        self.assertEqual(paginate(list(range(10)), 4, 3), [9])
+        self.assertEqual(paginate(list(range(9)), 3, 3), [6, 7, 8])
+
+    def test_out_of_range(self):
+        self.assertEqual(paginate(list(range(3)), 5, 3), [])