The refresh button turns while its feed is checked (#78)

The feed events already put a spinner on the sidebar row, which a phone
hides. The same state now sets scan-this (the open feed, or a feed in the
open folder) and scan-any (any of your feeds) on <body>, and the refresh
icons turn under them. On <body> because the feed page is redrawn as items
come in.

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

CHANGELOG.md

@@ -10,6 +10,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - A feed that has no artwork of its own shows its website's icon instead.
+- The refresh button turns while its feed is being checked, and the check-every-feed buttons
+  while any of yours is.
 - Adding a website's address subscribes to the feed that site links, instead of failing on every scan.
 - `/api/status` gives the number of feeds, items waiting to download and files downloaded, and
   the version, for a dashboard such as Homepage.