feat(config): add enable_thinking flag (default False) + fix HMMT bench gold answers

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/bench_hmmt.py

@@ -21,7 +21,7 @@ _HMMT_2025_SUBSET = [
     {
         "id": "hmmt-1",
         "question": "Find the number of positive integers n <= 100 such that n^2 + n is divisible by 6.",
-        "answer": "100",
+        "answer": "66",
     },
     {
         "id": "hmmt-2",
@@ -41,7 +41,7 @@ _HMMT_2025_SUBSET = [
     {
         "id": "hmmt-5",
         "question": "What is the remainder when 2^100 is divided by 125?",
-        "answer": "76",
+        "answer": "1",
     },
 ]