feat: 添加 AI 索引重建功能，优化相关 API 和工作流，增强内存管理配置

backend/src/controllers/admin_api.rs

@@ -230,8 +230,8 @@ pub struct AdminSiteSettingsResponse {
 
 #[derive(Clone, Debug, Serialize)]
 pub struct AdminAiReindexResponse {
-    pub indexed_chunks: usize,
-    pub last_indexed_at: Option<String>,
+    pub queued: bool,
+    pub job: worker_jobs::WorkerJobRecord,
 }
 
 #[derive(Clone, Debug, Deserialize)]
@@ -1395,15 +1395,30 @@ pub async fn update_site_settings(
 
 #[debug_handler]
 pub async fn reindex_ai(headers: HeaderMap, State(ctx): State<AppContext>) -> Result<Response> {
-    check_auth(&headers)?;
-    let summary = ai::rebuild_index(&ctx).await?;
+    let actor = check_auth(&headers)?;
+    let job = worker_jobs::queue_ai_reindex_job(
+        &ctx,
+        Some(actor.username.clone()),
+        Some(actor.source.clone()),
+        None,
+        Some("manual".to_string()),
+    )
+    .await?;
+
+    admin_audit::log_event(
+        &ctx,
+        Some(&actor),
+        "worker.ai_reindex",
+        "worker_job",
+        Some(job.id.to_string()),
+        Some(job.worker_name.clone()),
+        None,
+    )
+    .await?;
 
     format::json(AdminAiReindexResponse {
-        indexed_chunks: summary.indexed_chunks,
-        last_indexed_at: format_timestamp(
-            summary.last_indexed_at.map(Into::into),
-            "%Y-%m-%d %H:%M:%S UTC",
-        ),
+        queued: true,
+        job,
     })
 }