竞赛演示模式：首屏降噪与预置导览

- demo_mode 配置项（默认开）：不弹初始设置，LLM/语义警告横幅降级为顶栏状态点
- 顶栏新增'开始演示'导览（驾驶舱→新岗位发现→Java演化→匹配诊断四步预置路线）
- 图谱默认降噪：场景/行业图层默认关、关系标签默认关（悬停/缩放显示）
- 演化页默认锁定 Java 强样例；数据版本徽标标注'（模拟）'；联系方式移入设置页
- start.bat/start.sh 启动脚本

app/api/routes.py

@@ -93,6 +93,7 @@ def health() -> dict:
                 "llm_ready": ready, "offline_fallback": not ready,
                 "embed": semantic.status(_cfg),
                 "guided": bool(_cfg.get("guided")),
+                "demo_mode": bool(_cfg.get("demo_mode", True)),
                 "mode": "online" if ready else "offline"})
 
 
@@ -221,6 +222,7 @@ class ConfigBody(BaseModel):
     embed_api_base_url: str | None = None
     embed_api_model: str | None = None
     guided: bool | None = None           # 初始设置引导完成标记
+    demo_mode: bool | None = None        # 竞赛演示模式开关
     mode: str | None = None              # demo | live
 
 
@@ -243,6 +245,7 @@ def _public_config() -> dict:
         },
         "embed": semantic.status(_cfg),
         "mode": str(_cfg.get("mode", "demo")),
+        "demo_mode": bool(_cfg.get("demo_mode", True)),
         "offline_fallback": not ready,
     }
 
@@ -290,15 +293,17 @@ def save_config(body: ConfigBody) -> dict:
         updates["embed_api_model"] = body.embed_api_model.strip()
     if body.guided is not None:
         updates["guided"] = bool(body.guided)
+    if body.demo_mode is not None:
+        updates["demo_mode"] = bool(body.demo_mode)
 
     save_runtime_settings(updates)
     # 热生效：令牌、模式与 LLM/语义模型配置立即更新到运行配置（下次调用即读取）
     for k in ("access_token", "mode", "llm_api_key", "llm_base_url", "llm_model",
               "embed_model_path", "embed_provider", "embed_api_key",
-              "embed_api_base_url", "embed_api_model", "guided"):
+              "embed_api_base_url", "embed_api_model", "guided", "demo_mode"):
         if k in updates:
-            if updates[k]:
-                _cfg[k] = updates[k]
+            if updates[k] or isinstance(updates[k], bool):
+                _cfg[k] = updates[k]     # 布尔 False 也要写入（如关闭演示模式）
             else:
                 _cfg.pop(k, None)
     logger.info("运行时设置已保存到 config.json: %s", sorted(updates))