The refresh buttons keep turning between one feed and the next (#231)

A scan checks its feeds one at a time; in the gap between two the body class came off, the
icon snapped back upright and the spin restarted, many times a second with fetches ahead.
The class now comes off only after 600 ms with nothing being checked.

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

web/CHANGELOG.md

@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- The check-every-feed button turns smoothly through a scan instead of jerking back upright between one feed and the next (#231).
+
 ## [1.0.1] - 2026-10-13
 
 ### Fixed