Optimize tag cloud query

Still does a sort that ought to be indexable, but fixing that would be considerably more work.

index.js

@@ -288,14 +288,15 @@ async function getCategories(db) {
 
 async function getTagCloud(db, limit, offset=0) {
   const tags = db.prepare(`
-    SELECT count(t.id) as c, t.name
-    FROM article__tag a_t
-    LEFT JOIN article a ON a_t.article_id = a.id
-    LEFT JOIN tag t ON a_t.tag_id = t.id
-    GROUP BY t.id
-    ORDER BY c DESC
+    SELECT name, count FROM (
+    SELECT tag_id, COUNT(1) AS count
+    FROM article__tag
+    GROUP BY tag_id
+    ORDER BY count DESC
     LIMIT @limit
     OFFSET @offset
+    )
+    INNER JOIN tag on tag_id = tag.id
   `).all({ limit, offset })
   return tags
 }