feat(embeds): interactive X/Twitter post embed + Apple Music player

X/Twitter: the static OG card was a snapshot — no video, no galleries/threads.
Keep it as the (reliable) facade and add a 'View post' button that loads the
official platform.twitter.com interactive embed on click: playable video/GIF,
image galleries, quote tweets. The embed self-sizes via a scoped postMessage
resize listener (matched to our iframe + the platform.twitter.com origin). Nothing
loads from X until the user clicks, and the link still works if X blocks the frame.

Apple Music: music.apple.com album/playlist/song links now play inline via the
embed.music.apple.com player (compact for a single song, tall for collections),
through the existing MediaEmbedCard audio path.

Pure parsers/builders unit-tested (13 cases). Desktop CSP frame-src adds
platform.twitter.com + embed.music.apple.com (separate commit).

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

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

@@ -257,6 +257,16 @@ export const EmbedIframe = style([
   },
 ]);
 
+// Variable-height iframe that sizes itself (X/Twitter post embed — height set inline).
+export const EmbedIframeStatic = style([
+  DefaultReset,
+  {
+    width: '100%',
+    border: 0,
+    display: 'block',
+  },
+]);
+
 export const EmbedPlaceholder = style([
   DefaultReset,
   {
@@ -415,6 +425,11 @@ export const BadgeStreamable = style({
   color: '#ffffff',
 });
 
+export const BadgeAppleMusic = style({
+  backgroundColor: '#fa243c',
+  color: '#ffffff',
+});
+
 // ---------------------------------------------------------------------------
 // Twitch LIVE badge
 // ---------------------------------------------------------------------------