Apple Podcasts' top charts into the directory weekly, and its categories checked (#252)

With apple_country set, the directory fetches Apple's top 100 podcasts and the top 50 of each of
its 19 categories for that country (itunes.apple.com/{cc}/rss/toppodcasts), looks up each
show's RSS address (/lookup, 100 ids a call, three seconds apart, as Apple asks for no more than
about twenty a minute), and stores them as the snapshot apple-podcasts with no subscribers. The
refresher fetches them like any feed; the most-subscribed chart is unchanged. Apple's primary
genre goes in as the snapshot's category, used only while a feed names none.

The same weekly run reads Apple's genre tree (ws/genres?id=26) and warns when it differs from
ipx_feed's CATEGORIES; on 2026-10-15 they were the same, all 19 and their subcategories.

A syncs table keeps when it last ran: at start if a week has passed, again weekly, an hour after
a failure. keep_instances spares apple-podcasts, which no token holds, and no token may take
the name. A trace a sync, a span each answer.

CLAUDE.md: builds one cargo command at a time, the load looked at before and after, after a
build chained with a test compile took Tower past 200.

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

crates/feed/src/lib.rs

@@ -1120,6 +1120,11 @@ const ALIASES: &[(&str, &str)] =
 /// 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.
+/// Apple's categories as ipx has them, for the directory to check against Apple's own (#252).
+pub fn categories() -> &'static [(&'static str, &'static [&'static str])] {
+    CATEGORIES
+}
+
 pub fn category_path(name: &str) -> (String, Option<String>) {
     // A feed's own text, which can end in a stray comma: "Soccer," was a category of its own.
     let name = name.trim().trim_end_matches([',', ';', '.']).trim_end();