fix(pwa): keep PWA alive during TG login (anchor opens Telegram, app polls on /tg-wait)

window.location.href=deep_link navigated the whole PWA to t.me, destroying the
/tg-wait polling screen -> the authenticated token was never fetched. Prefetch
the pairing session and open Telegram via an <a href> (OS app-switch, PWA stays
mounted polling); add an Open-Telegram fallback link on the wait screen.

Co-Authored-By: claude-flow <ruv@ruv.net>

driver-pwa/frontend/src/pages/LoginPage.tsx

@@ -1,4 +1,4 @@
-import { useState } from "react";
+import { useEffect, useState } from "react";
 import { useNavigate } from "react-router-dom";
 import { toast } from "sonner";
 import { authRequest, authVerify, tgSession } from "@/api/driver";
@@ -15,19 +15,23 @@ export function LoginPage() {
   const [channel, setChannel] = useState<string>("");
   const [busy, setBusy] = useState(false);
   const [mode, setMode] = useState<"choose" | "code">("choose");
+  // Prefetched pairing session so the «Войти через Telegram» control is a real
+  // <a href> the OS opens in Telegram (a synchronous user gesture) WITHOUT
+  // navigating the PWA away — the app stays mounted on /tg-wait and polls.
+  const [tg, setTg] = useState<{ pair_session: string; deep_link: string | null } | null>(null);
   const e164 = "7" + phone;
 
-  async function loginViaTelegram() {
-    setBusy(true);
-    try {
-      const r = await tgSession();
-      sessionStorage.setItem("pp-pair-session", r.pair_session);
-      if (r.deep_link) { window.location.href = r.deep_link; }
-      nav("/tg-wait");
-    } catch {
-      toast.error("Не удалось начать вход. Попробуйте «по коду».");
-      setBusy(false);
-    }
+  useEffect(() => {
+    let alive = true;
+    tgSession().then((r) => { if (alive) setTg(r); }).catch(() => {});
+    return () => { alive = false; };
+  }, []);
+
+  function startTg() {
+    if (!tg) return;
+    sessionStorage.setItem("pp-pair-session", tg.pair_session);
+    if (tg.deep_link) sessionStorage.setItem("pp-pair-deeplink", tg.deep_link);
+    nav("/tg-wait");
   }
 
   async function requestCode() {
@@ -75,9 +79,21 @@ export function LoginPage() {
 
       {mode === "choose" ? (
         <>
-          <button className="btn-primary" disabled={busy} onClick={loginViaTelegram}>
-            {busy ? <Spinner /> : "Войти через Telegram"}
-          </button>
+          {tg?.deep_link ? (
+            <a
+              href={tg.deep_link}
+              target="_blank"
+              rel="noopener noreferrer"
+              className="btn-primary block text-center"
+              onClick={startTg}
+            >
+              Войти через Telegram
+            </a>
+          ) : (
+            <button className="btn-primary" disabled>
+              <Spinner />
+            </button>
+          )}
           <p className="text-muted text-xs mt-3">Telegram подтвердит ваш номер автоматически.</p>
           <button className="btn-ghost mt-4" onClick={() => setMode("code")}>Войти по коду</button>
         </>