Send a changed feed's row to the page instead of it reloading the list (#105)

After a feed was checked, failed or downloaded a file, and after every item read, the page
fetched /api/feeds whole, about 60 ms for 160 rows, though one row had changed. The live event
stream now knows who is connected and, after an event that changes a feed, sends that person
its row (feed_row), built by the same code as the list (feed_rows, with Db::feed_list asked for
one feed). Marking an item read answers with the feed's row. The page puts the row in place
and redraws once a frame. A routine skip of a feed not due sends nothing.

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

web/src/items.ts

@@ -153,7 +153,7 @@ function setRead(e,read){
   const w: {read: boolean, done?: number}={read}; readWrites.set(readKey(e),w);
   return api(`/api/entries/${encodeURIComponent(e.feed_id)}/${encodeURIComponent(e.guid)}/flags`,
       {method:'POST',body:JSON.stringify({read})})
-    .then(()=>{ w.done=performance.now(); loadFeeds(true); });
+    .then(row=>{ w.done=performance.now(); if(row) patchFeed(row); });
 }
 
 /// Opening an item is reading it. The row is redrawn where it stands rather than the list