docs(embeds): SoundCloud short links already embed via og:url (#200)

The comment said on.soundcloud.com links need an oEmbed round-trip. They
don't: Synapse follows the redirect for the preview and the og:url
fallback re-parses the canonical track URL. Checked with a real short
link (the play facade loads the w.soundcloud player).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/utils/videoEmbed.ts

@@ -363,9 +363,11 @@ const SOUNDCLOUD_PROFILE_TABS = new Set([
 export function isSoundCloudTrack(url: string): boolean {
   try {
     const { hostname, pathname } = new URL(url);
-    // NOTE: on.soundcloud.com short links are NOT handled here — the w.soundcloud
-    // widget resolver doesn't follow the redirect; supporting them needs an oEmbed
-    // round-trip (soundcloud.com/oembed is CORS-enabled) to get the canonical URL.
+    // on.soundcloud.com short links are not matched here (the w.soundcloud widget
+    // doesn't follow the redirect), but they still embed: Synapse follows the
+    // redirect when building the preview, and UrlPreviewCard's og:url fallback
+    // re-parses the canonical soundcloud.com/<artist>/<track> URL (verified with
+    // a real short link, Gitea #200).
     if (hostname.replace(/^www\./, '') !== 'soundcloud.com') return false;
     // /<artist>/<track|sets/set> — at least two segments, not a bare profile
     const parts = pathname