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/ipc.rs

@@ -15,6 +15,9 @@ pub enum Event {
     FeedSkip { feed: String, reason: String },
     FeedDone { feed: String, new: usize, downloaded: usize, failed: usize, torrents: usize },
     FeedError { feed: String, msg: String },
+    /// The feed answered from a new address after redirects that all said it moved for good,
+    /// and the catalogue now has that address (#115).
+    FeedMoved { feed: String, from: String, to: String },
     Progress {
         feed: String,
         /// Which enclosure this is about. Without it a UI cannot tell one download's
@@ -50,6 +53,7 @@ impl Event {
                 "{feed}: {new} new entries, {downloaded} downloaded, {failed} failed, {torrents} torrents deferred"
             ),
             Event::FeedError { feed, msg } => format!("{feed}: error: {msg}"),
+            Event::FeedMoved { feed, from, to } => format!("{feed}: moved for good from {from} to {to}; following it"),
             Event::Progress { file, done, total, .. } => match total {
                 Some(t) if *t > 0 => format!(
                     "    {file}: {:.1}% ({:.1}/{:.1} MB)",
@@ -172,7 +176,7 @@ fn log_event(e: &Event, wire: bool) {
         ($level:ident, $target:literal, $text:expr) => {
             tracing::$level!(
                 target: $target,
-                ev = s("ev"), feed = s("feed"), msg = s("msg"), url = s("url"), reason = s("reason"),
+                ev = s("ev"), feed = s("feed"), msg = s("msg"), url = s("url"), reason = s("reason"), from = s("from"), to = s("to"),
                 new = n("new"), downloaded = n("downloaded"), failed = n("failed"),
                 torrents = n("torrents"), bytes = n("bytes"), feeds = n("feeds"),
                 pending = n("pending"), enclosure = n("enclosure"), files = n("files"),
@@ -328,6 +332,14 @@ pub async fn proxy(path: &Path, cmd: &Command) -> Result<()> {
 mod tests {
     use super::*;
 
+    #[test]
+    fn a_feed_that_moved_says_so_on_the_wire_and_in_words() {
+        let e = Event::FeedMoved { feed: "x".into(), from: "http://a/f".into(), to: "https://a/f".into() };
+        let wire = serde_json::to_value(&e).unwrap();
+        assert_eq!((wire["ev"].as_str(), wire["from"].as_str(), wire["to"].as_str()), (Some("feed_moved"), Some("http://a/f"), Some("https://a/f")));
+        assert_eq!(e.human().unwrap(), "x: moved for good from http://a/f to https://a/f; following it");
+    }
+
     #[test]
     fn commands_parse_from_the_wire_form() {
         let got: Command = serde_json::from_str(r#"{"cmd":"fetch"}"#).unwrap();