config: add baidu_search example to config.example.json (#1990)

Add Baidu Qianfan AI Search configuration block after glm_search,
matching the BaiduSearchConfig struct defaults (enabled: false,
max_results: 10).

Co-authored-by: BeaconCat <BeaconCat@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

config/config.example.json

@@ -286,6 +286,12 @@
         "search_engine": "search_std",
         "max_results": 5
       },
+      "baidu_search": {
+        "enabled": false,
+        "api_key": "",
+        "base_url": "https://qianfan.baidubce.com/v2/ai_search/web_search",
+        "max_results": 10
+      },
       "fetch_limit_bytes": 10485760,
       "private_host_whitelist": []
     },