Refresh buttons turn from the press to the end of their scan; quick checks keep the count (#232, #233)

The buttons followed the feeds being checked, so they stopped between one feed and the next;
7ecbe82 held them for 600 ms over each gap. Now pressing one starts it, and scan_done stops
it only when it is the end of the scan asked for: scan_done carries `only` and `forced`, so a
scheduled scan finishing first does not stop a button whose scan is queued behind it. An
error event, a job that failed without a scan_done, stops them all.

A row's spinner stood in for its unread count from the moment its feed was checked; most
checks take milliseconds, so each count blinked as the scan went by. It now waits 300 ms.

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

web/src/events.ts

@@ -66,7 +66,9 @@ function connect(){
     // every open page reloaded the whole list each time (#103).
     // Rows came as feed_row events. ponytail: a feed an OPML drops stays in the list until the
     // page reloads; reload the list here when a scan synced an OPML if that ever matters.
-    else if(ev.ev==='scan_done'){ scanning.clear(); paintScanning(); if(ev.feeds) refreshEntries(); }
+    else if(ev.ev==='scan_done'){ scanning.clear(); paintScanning(); spinEnd(ev); if(ev.feeds) refreshEntries(); }
+    // The worker's job failed, so the scan someone is waiting on will send no scan_done.
+    else if(ev.ev==='error') spinEnd();
   };
   sse.onerror=()=>{ sse.close(); dropped=true; setTimeout(connect,4000); };
 }