feat(ui): real friend-invite share with a per-bot link

The friend-code 'share' was an <a> that just opened the bot. Make it a real share:
Telegram's native share-to-chat picker inside the Mini App (openTelegramLink +
t.me/share/url), the system share sheet (navigator.share) on the web, else copy the
link. The shared deep link points at the same bot the player is in — it picks
VITE_TELEGRAM_LINK_EN/_RU by the session's service language, falling back to the
single VITE_TELEGRAM_LINK. Adds the per-bot build args across Dockerfile / compose /
ci.yaml / .env / docs; PLAN TODO-5 updated.

ui/src/lib/telegram.ts

@@ -15,6 +15,7 @@ interface TelegramWebApp {
   contentSafeAreaInset?: { top: number; bottom: number; left: number; right: number };
   ready?: () => void;
   expand?: () => void;
+  openTelegramLink?: (url: string) => void;
   onEvent?: (event: string, handler: () => void) => void;
   setHeaderColor?: (color: string) => void;
   setBackgroundColor?: (color: string) => void;
@@ -49,6 +50,19 @@ export function insideTelegram(): boolean {
   return !!w && typeof w.initData === 'string' && w.initData.length > 0;
 }
 
+/**
+ * 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
+ * Telegram or when the SDK lacks the method, so the caller can fall back to the Web
+ * Share API. Works consistently on iOS and Android within Telegram.
+ */
+export function shareTelegramLink(url: string, text: string): boolean {
+  const w = webApp();
+  if (!w?.openTelegramLink) return false;
+  w.openTelegramLink(`https://t.me/share/url?url=${encodeURIComponent(url)}&text=${encodeURIComponent(text)}`);
+  return true;
+}
+
 /** TelegramLaunch is the data a Mini App launch carries. */
 export interface TelegramLaunch {
   initData: string;