fix(embeds): animate GIF previews; add Mixcloud/Deezer; misc embed fixes

GIF previews rendered but never played: Synapse's /thumbnail endpoint
flattens animated GIFs to a still first frame. GifCard and the generic OG
card now request the original via /download (no width/height) for GIFs, so
they animate. Guarded with shouldServeGifOriginal(): a matrix:image:size cap
(10 MB) keeps a huge self-hosted GIF on the frozen thumbnail, and the generic
card's eager <img> gains loading="lazy" (it was the one preview image missing
it) so originals stay off the wire until near the viewport.

Also adds Mixcloud + Deezer inline media embeds (iframe widgets via
parseMediaEmbed/MediaEmbedCard, matching the existing click-to-play pattern),
and fixes Deezer podcast links: they live at /show/<id>, not /podcast/<id>
(the latter 404s on Deezer's own oEmbed) — verified against the live API.

Reviewed by two agents; both findings (Deezer /show, GIF eager-load) fixed
and covered by tests. Desktop Tauri frame-src CSP updated separately.

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

src/app/components/url-preview/UrlPreview.css.tsx

@@ -549,6 +549,16 @@ export const BadgeTidal = style({
   color: '#ffffff',
 });
 
+export const BadgeMixcloud = style({
+  backgroundColor: '#52aad8',
+  color: '#ffffff',
+});
+
+export const BadgeDeezer = style({
+  backgroundColor: '#a238ff',
+  color: '#ffffff',
+});
+
 // ---------------------------------------------------------------------------
 // Twitch LIVE badge
 // ---------------------------------------------------------------------------

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

@@ -305,6 +305,32 @@ function isTenor(url: string): boolean {
   }
 }
 
+// Synapse's thumbnailer flattens animated images to a single still frame, so a
+// GIF served from /thumbnail renders but never plays. Detect GIF previews so the
+// card can point at /download (the original) instead.
+function isGifPreview(url: string, prev: IPreviewUrlResponse): boolean {
+  if (prev['og:image:type'] === 'image/gif') return true;
+  try {
+    return new URL(url).pathname.toLowerCase().endsWith('.gif');
+  } catch {
+    return false;
+  }
+}
+
+// Ceiling on the /download upgrade below: a self-hosted GIF can be hundreds of
+// MB, and unlike a thumbnail it is served unscaled. Past the cap we keep the
+// (frozen) thumbnail — the card still links out, so the GIF is one click away.
+const GIF_ORIGINAL_MAX_BYTES = 10 * 1024 * 1024;
+
+// Should this preview's image be fetched whole (so it animates) rather than
+// thumbnailed? Size is advisory: Synapse usually reports it, and when it's
+// absent we prefer a working animation over a hypothetical huge file.
+function shouldServeGifOriginal(url: string, prev: IPreviewUrlResponse): boolean {
+  if (!isGifPreview(url, prev)) return false;
+  const size = prev['matrix:image:size'];
+  return typeof size !== 'number' || size <= GIF_ORIGINAL_MAX_BYTES;
+}
+
 function getCardVariant(url: string): CardVariant {
   // NOTE: embeddable providers (YouTube/Vimeo/TikTok/Spotify/Twitch/…) are handled
   // upstream by parseMediaEmbed + MediaEmbedCard; getCardVariant only routes the
@@ -1077,6 +1103,8 @@ const EMBED_BADGE: Record<string, { label: string; class: string }> = {
   bluesky: { label: 'Bluesky', class: previewCss.BadgeBluesky },
   loom: { label: 'Loom', class: previewCss.BadgeLoom },
   kick: { label: 'Kick', class: previewCss.BadgeKick },
+  mixcloud: { label: 'Mixcloud', class: previewCss.BadgeMixcloud },
+  deezer: { label: 'Deezer', class: previewCss.BadgeDeezer },
 };
 
 // The homeserver preview for some sites (notably Reddit) comes back as a bot-check
@@ -2081,8 +2109,13 @@ function GifCard({
   const title = (prev['og:title'] as string | undefined) ?? '';
   const mxcImage = prev['og:image'] as string | undefined;
 
+  // A GIF card exists to show a moving GIF, so request the original rather than
+  // a thumbnail — the thumbnail endpoint would return a frozen first frame.
+  // `loading="lazy"` below keeps it off the wire until it's near the viewport.
   const thumbSrc = mxcImage
-    ? mxcUrlToHttp(mx, mxcImage, useAuthentication, 400, 200, 'scale', false)
+    ? shouldServeGifOriginal(url, prev)
+      ? mxcUrlToHttp(mx, mxcImage, useAuthentication)
+      : mxcUrlToHttp(mx, mxcImage, useAuthentication, 400, 200, 'scale', false)
     : null;
 
   // If there's no image, fall back to a generic-style layout
@@ -2180,6 +2213,7 @@ function GenericCard({
           src={displayThumb}
           alt={prev['og:title']}
           title={prev['og:title']}
+          loading="lazy"
           tabIndex={0}
           onKeyDown={(evt) => onEnterOrSpace(() => onOpenViewer())(evt)}
           onClick={onOpenViewer}
@@ -2349,16 +2383,11 @@ export const UrlPreviewCard = as<'div', { url: string; ts: number }>(
           // Generic fallback — skip empty cards
           if (!prev['og:title'] && !prev['og:description']) return null;
 
-          const thumbUrl = mxcUrlToHttp(
-            mx,
-            prev['og:image'] || '',
-            useAuthentication,
-            256,
-            256,
-            'scale',
-            false,
-          );
           const imgUrl = mxcUrlToHttp(mx, prev['og:image'] || '', useAuthentication);
+          // Show the original for GIFs so they animate; thumbnailing freezes them.
+          const thumbUrl = shouldServeGifOriginal(url, prev)
+            ? imgUrl
+            : mxcUrlToHttp(mx, prev['og:image'] || '', useAuthentication, 256, 256, 'scale', false);
 
           return (
             <GenericCard