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/utils/videoEmbed.test.ts

@@ -24,6 +24,9 @@ import {
   getBlueskyEmbed,
   getLoomId,
   getKickChannel,
+  getMixcloudFeed,
+  getDeezerEmbed,
+  deezerEmbedHeight,
   getSteamTarget,
   steamWidgetEmbedUrl,
   buildVideoEmbedUrl,
@@ -210,6 +213,58 @@ test('Apple Music: album vs single song height, embed host swap', () => {
   assert.equal(getAppleMusicEmbed('https://example.com/album/x/1'), null);
 });
 
+test('Mixcloud: cloudcast feed vs profile/section', () => {
+  assert.equal(
+    getMixcloudFeed('https://www.mixcloud.com/NTSRadio/some-show-2024/'),
+    'https://www.mixcloud.com/NTSRadio/some-show-2024/',
+  );
+  assert.equal(getMixcloudFeed('https://www.mixcloud.com/NTSRadio/'), null); // bare profile
+  assert.equal(getMixcloudFeed('https://www.mixcloud.com/NTSRadio/uploads/'), null); // profile tab
+  assert.equal(getMixcloudFeed('https://www.mixcloud.com/discover/house/'), null); // site section
+  assert.equal(getMixcloudFeed('https://example.com/a/b/'), null);
+  assert.ok(
+    parseMediaEmbed('https://www.mixcloud.com/NTSRadio/some-show/', HOST)?.embedUrl.startsWith(
+      'https://www.mixcloud.com/widget/iframe/?feed=',
+    ),
+  );
+});
+
+test('Deezer: track / album / playlist (+ locale prefix)', () => {
+  assert.deepEqual(getDeezerEmbed('https://www.deezer.com/track/3135556'), {
+    type: 'track',
+    id: '3135556',
+  });
+  assert.deepEqual(getDeezerEmbed('https://deezer.com/en/album/302127'), {
+    type: 'album',
+    id: '302127',
+  });
+  assert.deepEqual(getDeezerEmbed('https://www.deezer.com/us/playlist/1479458365?utm=x'), {
+    type: 'playlist',
+    id: '1479458365',
+  });
+  // Podcasts live at /show/<id>; /podcast/<id> is not a real Deezer path.
+  assert.deepEqual(getDeezerEmbed('https://www.deezer.com/us/show/1002330852'), {
+    type: 'show',
+    id: '1002330852',
+  });
+  assert.deepEqual(getDeezerEmbed('https://www.deezer.com/us/episode/897651701'), {
+    type: 'episode',
+    id: '897651701',
+  });
+  assert.equal(getDeezerEmbed('https://www.deezer.com/us/podcast/1002330852'), null);
+  assert.equal(getDeezerEmbed('https://www.deezer.com/'), null);
+  assert.equal(getDeezerEmbed('https://www.deezer.com/track/notanid'), null);
+  assert.equal(deezerEmbedHeight('track'), 152);
+  assert.equal(deezerEmbedHeight('episode'), 152);
+  assert.equal(deezerEmbedHeight('show'), 352);
+  assert.equal(deezerEmbedHeight('album'), 352);
+  assert.ok(
+    parseMediaEmbed('https://www.deezer.com/track/3135556', HOST)?.embedUrl.startsWith(
+      'https://widget.deezer.com/widget/dark/track/3135556',
+    ),
+  );
+});
+
 test('getSteamTarget: app / news / bundle / non-content', () => {
   assert.deepEqual(getSteamTarget('https://store.steampowered.com/app/739630/Phasmophobia/'), {
     kind: 'app',