A spinner on the feed being checked, not toasts; check only your own feeds

The scan's events reach everyone, so every browser showed "<feed>: N new" and
"Scanning…" toasts, and refreshed, for everyone's feeds. Now a feed's row, and
its folder's, carries a spinner between feed_start and its done, skip or error;
the list refreshes only for the reader's own feeds; the scan toasts are gone, and
"Downloaded" is said only for a file on screen.

"Check every feed" from the web UI sent a scan of every feed on the server.
Command::Fetch takes an optional `feeds` list -- those feeds and the feeds
inside any OPML among them -- and the web fills it with the asker's
subscriptions. The schedule and the CLI send none, meaning every feed.

Closes #37.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- A feed being checked shows a small spinner at the end of its row (and its folder's), instead of
+  toasts: no more "Scanning…" or "1 new" pop-ups, and none at all for feeds you do not read. A
+  "Downloaded" toast is only for a file on your screen.
+- "Check every feed" checks every feed you subscribe to, not every feed on the server.
+
 ## [0.8.0] - 2026-09-18
 
 ### Added