feat(browser-fetch): add lightpanda-backed fetch service and knowledge URL fallback

Adds a new browser-fetch microservice that wraps Lightpanda for rendering
JS-heavy pages, and wires it into the knowledge URL parser as a fallback
when the upstream link reader returns 403/429/5xx for an allow-listed
domain (e.g. zhuanlan.zhihu.com). Includes config/env plumbing, hot-reload
diff support, and full deploy assets (Dockerfile target, docker-compose,
k3s manifests, image-build/package scripts).

server/configs/config.local.yaml.example

@@ -204,3 +204,23 @@ generation:
   worker_concurrency: 8
   stream_enabled: false
   article_timeout: 8m
+
+browser_fetch:
+  enabled: false
+  provider: lightpanda
+  service_url: http://localhost:8082
+  token: dev-browser-fetch-token
+  queue_size: 64
+  worker_concurrency: 2
+  request_timeout: 45s
+  cache_ttl: 6h
+  allowed_domains:
+    - zhuanlan.zhihu.com
+    - zhihu.com
+  trigger_status:
+    - 403
+    - 429
+    - 500
+    - 502
+    - 503
+    - 504

server/configs/config.yaml

@@ -216,4 +216,24 @@ generation:
   task_recovery_batch_size: 100
   task_queued_stale_after: 2m
   task_max_attempts: 3
+
+browser_fetch:
+  enabled: false
+  provider: lightpanda
+  service_url: http://localhost:8082
+  token: dev-browser-fetch-token
+  queue_size: 64
+  worker_concurrency: 2
+  request_timeout: 45s
+  cache_ttl: 6h
+  allowed_domains:
+    - zhuanlan.zhihu.com
+    - zhihu.com
+  trigger_status:
+    - 403
+    - 429
+    - 500
+    - 502
+    - 503
+    - 504