fix(url-preview): thumbnail fallback + quiet timeline console spam

Two console-noise / glitch fixes surfaced while a room with link
previews was open:

- URL preview og:image thumbnails 400 when Synapse can't thumbnail a
  cached preview image (SVG/animated), leaving a broken image that the
  browser keeps re-requesting. GenericCard now falls back to the full
  image on error, then hides the image (and shows the link icon) if that
  also fails, so no broken image and no repeated failing requests.

- Extend the existing console.warn filter to drop matrix-js-sdk's
  high-volume, benign timeline bookkeeping warnings ("EventTimelineSet…"
  and "Decrypted event … is not in room …"), which fire constantly in
  E2EE rooms with threads. Real warnings still log.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/components/url-preview/UrlPreviewCard.tsx

@@ -1965,16 +1965,29 @@ function GenericCard({
   const description = prev['og:description'] ?? '';
   const siteName = typeof prev['og:site_name'] === 'string' ? prev['og:site_name'] : undefined;
 
+  // Synapse returns 400 from the thumbnail endpoint when it can't thumbnail a
+  // cached preview image (e.g. SVG/animated). Fall back to the full image, then
+  // hide entirely if that also fails — otherwise the card shows a broken image
+  // and the browser keeps re-requesting the failing thumbnail (console spam).
+  const [useFullImg, setUseFullImg] = useState(false);
+  const [imgFailed, setImgFailed] = useState(false);
+  const displayThumb = useFullImg ? imgUrl : thumbUrl;
+  const handleImgError = () => {
+    if (!useFullImg && imgUrl && imgUrl !== thumbUrl) setUseFullImg(true);
+    else setImgFailed(true);
+  };
+
   return (
     <>
-      {thumbUrl && (
+      {!imgFailed && displayThumb && (
         <UrlPreviewImg
-          src={thumbUrl}
+          src={displayThumb}
           alt={prev['og:title']}
           title={prev['og:title']}
           tabIndex={0}
           onKeyDown={(evt) => onEnterOrSpace(() => onOpenViewer())(evt)}
           onClick={onOpenViewer}
+          onError={handleImgError}
         />
       )}
       {imgUrl && (
@@ -1997,7 +2010,7 @@ function GenericCard({
           size="T200"
           priority="300"
         >
-          {!thumbUrl && (
+          {(!displayThumb || imgFailed) && (
             <Icon
               src={Icons.Link}
               size="50"