Trim the state database; Popular lists feeds the way Directory does

Drops the created columns on users, subscriptions and sessions, which were
written by every insert and read by nothing, and migrate()'s add list, whose
columns all predate 0.3.0. Removes Db::subscribed_feed_ids (no callers),
Db::subscriber_count (one caller wanting > 0) and Managed.orphaned (never
read). The old-database test now builds the tables with foreign keys on.

Popular now lists the feeds inside an OPML or a Patreon creator, never the
collection, as Directory does.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TAC7sLVqfKmY6rsTLXzNgk

web/index.html

@@ -777,7 +777,7 @@ const VIEWS={
   ':directory':{title:'Directory',icon:ICON.directory,url:'/api/directory',
     blurb:'Every feed anyone on this server subscribes to, A to Z. The feeds inside an OPML are listed one by one, not the OPML.'},
   ':popular':{title:'Popular',icon:ICON.popular,url:'/api/popular',
-    blurb:'The ten feeds with the most subscribers here. An OPML counts as one feed.'},
+    blurb:'The ten feeds with the most subscribers here. The feeds inside an OPML count one by one, not the OPML.'},
   ':all':{title:'All Subscriptions',icon:ICON.all},
 };
 function renderFeeds(){