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/13-search-cent-rounding/repo/app/fin/tally.py

@@ -0,0 +1,3 @@
+def consolidate(lines):
+    """Sum line amounts and return the figure for the document footer."""
+    return round(sum(lines), 2)