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/runtime_config.go

@@ -26,6 +26,7 @@ type knowledgeRuntimeConfig struct {
 	ArkBaseURL         string
 	ArkAPIKey          string
 	URLMarkdownModel   string
+	BrowserFetch       config.BrowserFetchConfig
 }
 
 type generationStreamDisabledConfigProvider struct {
@@ -103,3 +104,14 @@ func knowledgeRuntimeFromConfig(retrievalCfg config.RetrievalConfig, llmCfg conf
 		URLMarkdownModel:   model,
 	}
 }
+
+func knowledgeRuntimeFromFullConfig(cfg *config.Config) knowledgeRuntimeConfig {
+	if cfg == nil {
+		return knowledgeRuntimeFromConfig(config.RetrievalConfig{}, config.LLMConfig{})
+	}
+	runtime := knowledgeRuntimeFromConfig(cfg.Retrieval, cfg.LLM)
+	browserFetch := cfg.BrowserFetch
+	config.NormalizeBrowserFetchConfig(&browserFetch)
+	runtime.BrowserFetch = browserFetch
+	return runtime
+}