feat(embeds): fallback for hung embeds and deleted X posts (#200)

Probed how real providers fail before picking signals:
- X renders an EMPTY frame for a deleted/private/suspended post and says
  so only via postMessage `twttr.private.no_results`. The post embed now
  swaps to "This post isn't available…" with an "Open on X" link.
- A hung frame never fires `load`. After 20 s every player (media, rich
  posts, TikTok, Steam widget, X) overlays "This embed is taking too long
  to load" with Retry (remounts the iframe) and "Open on <site>". A late
  `load` clears it.
- Instagram and Bluesky show their own "removed / not found" page, and a
  refused request still fires `load` (browser error page), so neither needs
  or can use a guess. A missing height message is not treated as failure.

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

src/app/utils/videoEmbed.ts

@@ -168,6 +168,33 @@ export function extractEmbedHeight(data: unknown): number | undefined {
   return undefined;
 }
 
+// How long an embed iframe may take to fire `load` before the card offers
+// Retry / "Open on …". Only a hang trips it: a frame whose request was refused,
+// or whose provider shows its own error page, still fires `load`.
+export const EMBED_LOAD_TIMEOUT_MS = 20_000;
+
+/**
+ * X's post embed (platform.twitter.com/embed/Tweet.html) renders an empty frame
+ * for a deleted, private or suspended post and reports it only via this
+ * postMessage: `{"twttr.embed": {"method": "twttr.private.no_results"}}`.
+ * `data` may be the raw string or the parsed object.
+ */
+export function isTwitterNoResults(data: unknown): boolean {
+  let d = data;
+  if (typeof d === 'string') {
+    try {
+      d = JSON.parse(d);
+    } catch {
+      return false;
+    }
+  }
+  if (!d || typeof d !== 'object') return false;
+  const tw = (d as { 'twttr.embed'?: unknown })['twttr.embed'];
+  if (!tw) return false;
+  const calls = (Array.isArray(tw) ? tw : [tw]) as Array<{ method?: string }>;
+  return calls.some((c) => c?.method === 'twttr.private.no_results');
+}
+
 export function tiktokPlayerEmbedUrl(id: string): string {
   // Pure 9:16 video player. music_info/description default OFF (they'd switch
   // TikTok to a wide "video + info panel" layout); controls/progress/play/volume/