Browse the Directory by category, then subcategory, as Apple does (#118)

The Directory had one row of chips holding whatever each feed's category was, a category
(Technology) or a subcategory (Tech News, Video Games) side by side: a podcast's own
<itunes:category> is stored as its subcategory, and Jev's answers (#117) are often
subcategories too, so after the first forced scan the row held 22 chips. /api/directory now
gives each feed's Apple category and subcategory, worked out from Apple's list, and the
page shows the categories, then a picked one's subcategories on a line of their own. A
category that is not Apple's, one an admin typed, stands as a category of its own.

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

src/web.rs

@@ -861,8 +861,10 @@ struct PopularRow {
     subscribers: i64,
     /// Yours already. Everyone counts, you included, so your own feeds are listed too.
     subscribed: bool,
-    /// The feed's own iTunes category, if it names one; most blogs do not.
+    /// Apple's category, from the feed's own iTunes category or else the catalogue's, and the
+    /// subcategory within it where there is one: the Directory browses them in that order.
     category: Option<String>,
+    subcategory: Option<String>,
     /// Any audio or video enclosure. Unlike category, every feed has an answer, so the
     /// Directory's Podcasts and Blogs between them hold everything.
     podcast: bool,
@@ -902,14 +904,16 @@ async fn popular(state: &WebState, user_id: i64, everything: bool) -> Result<Vec
         }
         let sum = listed.remove(&s.id).map(|l| l.summary).unwrap_or_default();
         let subscribed = mine.contains(&s.id);
+        // The feed's own wins; an admin's is for the feeds, mostly blogs, that name none.
+        let path = sum.category.or_else(|| s.cfg.category.clone()).map(|c| crate::feed::category_path(&c));
         out.push(PopularRow {
             id: s.id.clone(),
             title: sum.title,
             image: sum.image,
             subscribers: n,
             subscribed,
-            // The feed's own wins; an admin's is for the feeds, mostly blogs, that name none.
-            category: sum.category.or_else(|| s.cfg.category.clone()),
+            category: path.as_ref().map(|p| p.0.clone()),
+            subcategory: path.and_then(|p| p.1),
             podcast: media.contains(&s.id),
         });
     }