Announce a followed move as a feed_moved event (#115)

A feed moved to its new address was only logged by follow_move. It is now an event, feed_moved
with the feed and its old and new addresses, so it goes where every other event goes: the log,
with from and to as fields, the admin page's Scans view, `ipx fetch`, and the page, which gets
the feed's new row.

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

src/web.rs

@@ -1701,7 +1701,10 @@ async fn events(
 /// routine skip of a feed not due, dozens a minute that change nothing.
 fn changed_feed(ev: &Event) -> Option<&str> {
     match ev {
-        Event::FeedDone { feed, .. } | Event::FeedError { feed, .. } | Event::DownloadDone { feed, .. } => Some(feed),
+        Event::FeedDone { feed, .. }
+        | Event::FeedError { feed, .. }
+        | Event::FeedMoved { feed, .. }
+        | Event::DownloadDone { feed, .. } => Some(feed),
         Event::FeedSkip { feed, reason } if !reason.starts_with("not due") => Some(feed),
         _ => None,
     }