A spinner after pulling to refresh (#68)

Letting go of a pull removed its note at once and showed nothing else;
the sidebar's scanning spinner is hidden on a phone. With no sign the
check had started, people pulled again, and again. A "Checking for new
items" pill with a spinner now sits under the top bar until the request
is sent and two seconds have passed, and a pull meanwhile does nothing.
It lives outside #list, which a feed's render rebuilds.

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

CHANGELOG.md

@@ -26,6 +26,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Pulling the item list down to check for new items shows a spinner for a couple of seconds, and
+  a second pull meanwhile does nothing, instead of no sign at all that the check started.
 - Settings no longer lists the server's download folder, which only an admin can change, on
   the admin page.
 - On the Unread tab, a swipe back (or k) goes to the item you just read, instead of past it or