test(benchmarks): add concept-search tasks

Three tasks whose target code shares no vocabulary with the prompt, run in a
repository with generated distractor modules.

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

scripts/benchmarks/tasks/11-search-expired-evaluation/repo/app/ledger/archive.py

@@ -0,0 +1,8 @@
+from datetime import date
+
+
+def render_period_summary(account, period, today=None):
+    """Build the period summary document for an account."""
+    today = today or date.today()
+    lines = [f"{entry.label}: {entry.amount:.2f}" for entry in account.entries if entry.period == period]
+    return "\n".join(lines).encode()