feat(ui): route all in-app external links through Telegram openLink

Extend the openLink routing from the dictionary lookup to every external
link shown inside the Mini App, so none triggers the WebView's 'open this
link?' confirmation. A shared onExternalLinkClick handler resolves the anchor
via closest() (so it also works delegated on {@html} content), backed by a
pure routeExternalLinkInTelegram decision: only inside Telegram, only an
external http(s) target=_blank link, excluding same-origin/in-app and t.me
links (t.me keeps openTelegramLink). Applied to the word-check lookup, the
About rules link, the Feedback operator-reply links, and the feature-gated
announcement banner.

Outside Telegram every anchor keeps its native target=_blank.

ui/src/lib/telegram.ts

@@ -80,6 +80,48 @@ export function telegramOpenExternalLink(url: string): boolean {
   return true;
 }
 
+/**
+ * isExternalHttpUrl reports whether href is an absolute http(s) URL on a different origin than the
+ * app — so a same-origin or root-relative in-app (SPA) link is left to normal navigation, only a
+ * genuinely external link is routed through Telegram's browser.
+ */
+function isExternalHttpUrl(href: string): boolean {
+  try {
+    const u = new URL(href, typeof location === 'undefined' ? undefined : location.href);
+    if (u.protocol !== 'http:' && u.protocol !== 'https:') return false;
+    return typeof location === 'undefined' || u.origin !== location.origin;
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * routeExternalLinkInTelegram decides whether a clicked anchor should be opened through the Mini
+ * App SDK rather than the WebView's default navigation: only inside Telegram, and only for an
+ * external http(s) link opened in a new tab (target=_blank) that is not a t.me link (those use
+ * telegramOpenLink/openTelegramLink). Returns true when it opened the link through openLink — the
+ * caller should then preventDefault — and false to let the browser handle the click normally.
+ */
+export function routeExternalLinkInTelegram(anchor: { href: string; target: string }): boolean {
+  if (!insideTelegram()) return false;
+  if (anchor.target !== '_blank') return false;
+  if (anchor.href.startsWith('https://t.me/')) return false;
+  if (!isExternalHttpUrl(anchor.href)) return false;
+  return telegramOpenExternalLink(anchor.href);
+}
+
+/**
+ * onExternalLinkClick is the anchor click handler that applies routeExternalLinkInTelegram. It
+ * resolves the clicked anchor with closest(), so it works both attached directly on an <a> and
+ * delegated on a container that renders links (e.g. {@html} markdown). Attach it as onclick on an
+ * external link or its container; outside Telegram it is a no-op and the anchor's own
+ * target=_blank handles the click.
+ */
+export function onExternalLinkClick(e: MouseEvent): void {
+  const a = (e.target as HTMLElement | null)?.closest('a');
+  if (a && routeExternalLinkInTelegram(a)) e.preventDefault();
+}
+
 /**
  * shareTelegramLink opens Telegram's native "share to a chat" picker for url with a
  * caption, through the Mini App SDK (https://t.me/share/url). Returns false outside