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/feed.rs

@@ -1033,6 +1033,21 @@ const CATEGORIES: &[(&str, &[&str])] = &[
     ("TV & Film", &["After Shows", "Film History", "Film Interviews", "Film Reviews", "TV Reviews"]),
 ];
 
+/// Where a category sits in Apple's list, as (category, subcategory), so the Directory browses a
+/// category and then its subcategories as Apple's does (#118). A podcast's own is stored as its
+/// subcategory, and one an admin typed that is not Apple's stands as a category of its own.
+pub fn category_path(name: &str) -> (String, Option<String>) {
+    for (category, subs) in CATEGORIES {
+        if category.eq_ignore_ascii_case(name) {
+            return (category.to_string(), None);
+        }
+        if let Some(sub) = subs.iter().find(|s| s.eq_ignore_ascii_case(name)) {
+            return (category.to_string(), Some(sub.to_string()));
+        }
+    }
+    (name.to_string(), None)
+}
+
 /// A Directory category for a feed that names none of its own, which most blogs do not (#117):
 /// TypeSafe's Jev picks one of Apple's categories or subcategories from the feed's title and
 /// latest items, the subcategory being what a podcast's own category is stored as. The likeliest
@@ -1571,5 +1586,14 @@ mod tests {
         assert!(super::picked(&answer("Blogs")).is_err(), "not one of Apple's");
         assert!(super::picked(&serde_json::json!({"error": "rate limited"})).is_err());
     }
+
+    #[test]
+    fn category_path_finds_a_subcategory_s_category() {
+        use super::category_path;
+        assert_eq!(category_path("Tech News"), ("News".into(), Some("Tech News".into())));
+        assert_eq!(category_path("video games"), ("Leisure".into(), Some("Video Games".into())), "Apple's spelling");
+        assert_eq!(category_path("Technology"), ("Technology".into(), None));
+        assert_eq!(category_path("Homebrew"), ("Homebrew".into(), None), "not Apple's: its own category");
+    }
 }