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/internal/tenant/app/knowledge_service.go

@@ -49,6 +49,8 @@ type KnowledgeService struct {
 	jobs            chan knowledgeParseJob
 	cleanupMu       sync.Mutex
 	cleanupInFlight map[string]struct{}
+	browserFetchMu  sync.Mutex
+	browserFetchQ   *browserFetchQueue
 }
 
 type knowledgeParseJob struct {
@@ -199,7 +201,7 @@ func (s *KnowledgeService) WithConfigProvider(provider runtimeConfigProvider) *K
 func (s *KnowledgeService) runtimeConfig() knowledgeRuntimeConfig {
 	if s != nil && s.configProvider != nil {
 		if cfg := s.configProvider.Current(); cfg != nil {
-			return knowledgeRuntimeFromConfig(cfg.Retrieval, cfg.LLM)
+			return knowledgeRuntimeFromFullConfig(cfg)
 		}
 	}
 	if s == nil {