Auto-reindex channel on page visit if stale

GET /channels/{id} now fires a background _index_channel_task if the
channel hasn't been crawled in the last hour. The frontend refetches
channel + videos 8s after page load to pick up the updated data.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/Channel.jsx

@@ -1,4 +1,4 @@
-import { useState, useMemo } from "react";
+import { useState, useMemo, useEffect, useRef } from "react";
 import { useParams } from "react-router-dom";
 import { useQuery, useMutation, useQueryClient } from "@tanstack/react-query";
 import { getChannel, getChannelVideos, followChannel, unfollowChannel, indexChannel, downloadChannel } from "../api";
@@ -41,6 +41,18 @@ export default function ChannelPage() {
     queryFn: () => getChannelVideos(id).then((r) => r.data),
   });
 
+  // Refetch after the background re-index has had time to run
+  const refetchedRef = useRef(false);
+  useEffect(() => {
+    if (!id || refetchedRef.current) return;
+    refetchedRef.current = true;
+    const t = setTimeout(() => {
+      qc.invalidateQueries({ queryKey: ["channel", id] });
+      qc.invalidateQueries({ queryKey: ["channel-videos", id] });
+    }, 8000);
+    return () => clearTimeout(t);
+  }, [id, qc]);
+
   const followMut = useMutation({
     mutationFn: () =>
       channel?.status === "followed" ? unfollowChannel(id) : followChannel(id),