fix(question_gen): Information Synopsis 去重阈值放宽至 0.90

该题型天然高相似（benchmark 均值 0.66，中位数 0.67），
通用阈值 0.75/0.85 导致几乎所有新题被误判重复。
按题型覆盖为 0.90，只拦截真正的复制品。

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tools/generate_questions.py

@@ -811,6 +811,11 @@ async def _run_generate(args: argparse.Namespace) -> None:
     output_dir = Path(args.output_dir)
     per_type = args.per_type
     similarity_threshold = args.similarity_threshold
+    # Information Synopsis 题目天然高相似（均值 0.66，中位数 0.67），
+    # 用通用阈值会导致几乎所有新题被误判重复。按题型放宽。
+    _PER_TYPE_THRESHOLD = {
+        "Information Synopsis": max(similarity_threshold, 0.90),
+    }
     max_retries = args.max_retries
     concurrency = args.concurrency
     seed = args.seed
@@ -951,7 +956,7 @@ async def _run_generate(args: argparse.Namespace) -> None:
                 if (
                     pool.ndim == 2
                     and pool.shape[0] > 0
-                    and is_duplicate(candidate.question, pool, embed_fn, similarity_threshold)
+                    and is_duplicate(candidate.question, pool, embed_fn, _PER_TYPE_THRESHOLD.get(task_type, similarity_threshold))
                 ):
                     logger.warning("去重: {} 与池中题目相似", candidate.question_id)
                     continue