chore(browser-fetch): enable lightpanda by default and widen allowlist

Turn the lightpanda-backed fetch service on, bump worker concurrency to
3, and add baidu.com plus weixin.sogou.com to the allowed domains so the
knowledge URL fallback can resolve those sources without a config edit.

server/configs/config.yaml

@@ -218,17 +218,19 @@ generation:
   task_max_attempts: 3
 
 browser_fetch:
-  enabled: false
+  enabled: true
   provider: lightpanda
   service_url: http://localhost:8082
   token: dev-browser-fetch-token
   queue_size: 64
-  worker_concurrency: 2
+  worker_concurrency: 3
   request_timeout: 45s
   cache_ttl: 6h
   allowed_domains:
     - zhuanlan.zhihu.com
     - zhihu.com
+    - baidu.com
+    - weixin.sogou.com
   trigger_status:
     - 403
     - 429