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/main.rs

@@ -1374,6 +1374,7 @@ enum Outcome {
 /// is left alone, since the OPML would only put the old address back; so is a move onto an
 /// address another feed already has.
 async fn follow_move(ctx: &Ctx, id: &str, to: &str) -> Result<()> {
+    // Said in the event below, not logged here: the event is the log line.
     if subscriptions(ctx).await?.iter().any(|s| s.id != id && feed::same_feed(&s.cfg.url, to)) {
         tracing::info!(feed = id, to, "the feed moved to an address another feed already has; leaving it");
         return Ok(());
@@ -1382,7 +1383,7 @@ async fn follow_move(ctx: &Ctx, id: &str, to: &str) -> Result<()> {
     let Some(f) = cfg.feeds.get_mut(id) else { return Ok(()) };
     let from = std::mem::replace(&mut f.url, to.to_owned());
     ctx.store_cfg(cfg).await?;
-    tracing::info!(feed = id, from, to, "the feed moved for good; following it to its new address");
+    ctx.out.emit(Event::FeedMoved { feed: id.to_owned(), from, to: to.to_owned() });
     Ok(())
 }