Move old items' http artwork to https too, for hosts the feed no longer names (#110)

The first pass only asked the hosts the feed's current body names. IGN's feed kept five 2009
items with artwork on assets1/assets2.ignimgs.com, which its feed no longer mentions, so they
stayed on http. A scan now also asks, once per host, the hosts of the feed's stored http
artwork (Db::http_images).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/main.rs

@@ -1430,7 +1430,11 @@ async fn scan_one(
     if let Some(art) = &parsed.image {
         parsed.image = Some(feed::prefer_https(&ctx.client, art, &mut secure).await);
     }
-    // Items stored before, which a scan does not write again, move with their host.
+    // Items stored before, which a scan does not write again, move with their host, and a host
+    // only they still name is asked too.
+    for art in ctx.db.http_images(id).await? {
+        feed::prefer_https(&ctx.client, &art, &mut secure).await;
+    }
     for (host, ok) in &secure {
         if *ok {
             ctx.db.secure_images(id, host).await?;