feat: 知识库一键后台保存 + 对话置顶仅首页 + 排行榜页面增强

- 知识库「保存」改为一键触发，无需填表；后端经 BackgroundTasks 异步沉淀到 wiki，点击立即返回 {queued:true}
- 对话列表置顶分区仅在第一页展示，翻页后不再重复顶置
- 公开/管理员排行榜页面重构与维度增强；排行榜页改为整页统一滚动

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

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

@@ -102,7 +102,11 @@ export async function searchKnowledge(query: string, limit = 8) {
 }
 
 export async function ingestThread(threadId: string, payload: IngestThreadPayload = {}) {
-  return parseResponse<{ note: KnowledgeNote; created: boolean }>(
+  return parseResponse<{
+    note?: KnowledgeNote;
+    created?: boolean;
+    queued?: boolean;
+  }>(
     await apiFetch(`${baseUrl()}/ingest/thread/${encodeURIComponent(threadId)}`, {
       method: "POST",
       headers: { "Content-Type": "application/json" },

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

@@ -70,6 +70,8 @@ export interface IngestThreadPayload {
   status?: KnowledgeStatus;
   tags?: string[];
   include_sources?: boolean;
+  /** When true the backend sediments asynchronously and returns immediately. */
+  background?: boolean;
 }
 
 export interface BatchIngestPayload {