ipx add --list or --category updates a feed the catalogue already has (#107)

It refused one already there ("already subscribed as ..."), so a feed added before listing
existed, such as CBC's, could not be put in the Directory.

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

src/main.rs

@@ -686,6 +686,19 @@ async fn add(
     let url = &feed::find_feed(&ctx.client, &feed::expand_input(url)).await?;
     // Includes feeds derived from an OPML, or the same show could be added twice.
     if let Some(existing) = subscriptions(ctx).await?.iter().find(|s| feed::same_feed(&s.cfg.url, url)) {
+        // Listing a feed the catalogue already has, or giving it a category, is the point of
+        // asking again: it changes those, and nothing else.
+        if let Some(f) = cfg.feeds.get_mut(&existing.id)
+            && (list || category.is_some())
+        {
+            f.listed |= list;
+            if category.is_some() {
+                f.category = category;
+            }
+            ctx.store_cfg(cfg).await?;
+            println!("{} is already in the catalogue; updated its Directory listing", existing.id);
+            return Ok(());
+        }
         anyhow::bail!("already subscribed as {:?}", existing.id);
     }
     let id = add_one(ctx, &mut cfg, url, folder, keywords).await?;