feat: 性能插桩、缓存清除端点、LLM top_p 与 JSON 强制输出

- chat_routes.py: 新增 8 阶段性能计时（stages_ms）+ SSE 输出
- sync_routes.py: 新增 POST /cache/clear 缓存清除端点
- engine.py: LLM 调用增加 top_p 参数
- intent_analyzer.py: response_format 加配置开关（INTENT_RESPONSE_FORMAT）

core/engine.py

@@ -82,7 +82,7 @@ try:
         CLUSTER_SEED_FLOOR, CLUSTER_MAX_BOOST_PER_SECTION, CLUSTER_MAX_SECTIONS,
         CLUSTER_SECTION_PREFIX_LEVELS,
         # 上下文与生成
-        LLM_TEMPERATURE, LLM_MAX_TOKENS, RECALL_MULTIPLIER,
+        LLM_TEMPERATURE, LLM_TOP_P, LLM_MAX_TOKENS, RECALL_MULTIPLIER,
         # FAQ 与黑名单
         FAQ_RECALL_TOP_K, FAQ_BOOST_AMOUNT, FAQ_DECAY_MONTHS, FAQ_DECAY_RATE, FAQ_DECAY_MAX,
         BLACKLIST_MIN_DISLIKES, BLACKLIST_CACHE_TTL,
@@ -2361,6 +2361,7 @@ class RAGEngine:
                 "",
                 MODEL,
                 temperature=LLM_TEMPERATURE,
+                top_p=LLM_TOP_P,
                 max_tokens=LLM_MAX_TOKENS,
                 messages=messages,
                 error_prefix="[错误]"