feat: 知识批量沉淀改为后台任务,避免 nginx 504

- /ingest/threads/batch 新增 background 参数(默认 true),立即返回 {queued:true}
- 抽取循环抽出 _run_batch_ingest,后台路径显式传入 created_by
- 前端知识库页与输入框、线程 hooks/types 配套调整
- config.yaml 上下文压缩测试值

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend-web/src/core/knowledge/types.ts

@@ -147,6 +147,13 @@ export interface BatchIngestPayload {
   include_sources?: boolean;
   skip_existing?: boolean;
   mode?: "summary" | "full";
+  /**
+   * When true (default), the backend runs the per-thread extraction loop in a
+   * background task and returns immediately (`queued:true`) instead of blocking
+   * the request until every thread is processed — which otherwise outlives the
+   * nginx gateway timeout and surfaces as a generic "request failed".
+   */
+  background?: boolean;
   /** Optional model override for knowledge extraction (null = configured default). */
   model_name?: string | null;
   /** Optional extraction-prompt template id (null = scope default). */
@@ -157,6 +164,8 @@ export interface BatchIngestPayload {
 
 export interface BatchIngestResult {
   ok: boolean;
+  /** True when the backend queued the batch as a background task (see payload). */
+  queued?: boolean;
   processed: number;
   created: number;
   skipped: number;