Wire up email verification flow for new signups

requireEmailVerification was enabled but no sendVerificationEmail was
configured — new users saw "check your email", never received anything,
and couldn't log in (403 shown as "wrong email or password").

- email.ts: add verification email template; welcome email no longer
  claims the account is "confirmed"
- auth.ts: configure emailVerification (send on signup, resend on
  unverified login attempt, auto sign-in after verification, 24h TTL)
- register route: callbackURL=/dashboard so the verify link lands in
  the cabinet
- login form: distinguish 403 (unverified — tell user a fresh link was
  sent) and 429 (rate limit) from wrong credentials

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/(auth)/login/login-form.tsx

@@ -10,17 +10,27 @@ export function LoginForm() {
   const [email, setEmail] = useState("");
   const [password, setPassword] = useState("");
   const [error, setError] = useState("");
+  const [needsVerification, setNeedsVerification] = useState(false);
   const [loading, setLoading] = useState(false);
 
   async function handleSubmit(e: React.FormEvent) {
     e.preventDefault();
     setError("");
+    setNeedsVerification(false);
     setLoading(true);
 
     const result = await signIn.email({ email, password });
 
     if (result.error) {
-      setError("Неверный email или пароль");
+      if (result.error.status === 403) {
+        // Креды верны, но email не подтверждён. Better Auth уже
+        // переотправил письмо подтверждения — сообщаем об этом.
+        setNeedsVerification(true);
+      } else if (result.error.status === 429) {
+        setError("Слишком много попыток входа. Подождите минуту и попробуйте снова.");
+      } else {
+        setError("Неверный email или пароль");
+      }
       setLoading(false);
       return;
     }
@@ -82,6 +92,18 @@ export function LoginForm() {
           placeholder="••••••••"
         />
       </div>
+      {needsVerification && (
+        <div
+          className="text-xs py-3 px-3 space-y-1"
+          style={{ border: "2px solid var(--border)", color: "var(--foreground)" }}
+        >
+          <p className="font-bold">Email не подтверждён</p>
+          <p style={{ color: "var(--muted-foreground)" }}>
+            Мы отправили новое письмо со ссылкой подтверждения на <strong>{email}</strong>.
+            Проверьте почту (и папку «Спам»), затем войдите снова.
+          </p>
+        </div>
+      )}
       {error && (
         <p className="text-sm" style={{ color: "var(--destructive)" }}>
           {error}