feat(auth): refresh tokens + remember me

Backend: add refresh JWT (30d, token_type claim), POST /auth/refresh
endpoint (rotates token pair), remember_me on login, JWT_REFRESH_EXPIRY_DAYS
env var. Extractors now reject refresh tokens on protected routes.

Frontend: sessionStorage for non-remembered sessions, localStorage +
refresh token for remembered sessions. Transparent 401 recovery in
api.ts (retry once after refresh). Remember me checkbox on login page
with security note when checked.

k-tv-frontend/app/(auth)/login/page.tsx

@@ -8,12 +8,13 @@ import { useConfig } from "@/hooks/use-channels";
 export default function LoginPage() {
   const [email, setEmail] = useState("");
   const [password, setPassword] = useState("");
+  const [rememberMe, setRememberMe] = useState(false);
   const { mutate: login, isPending, error } = useLogin();
   const { data: config } = useConfig();
 
   const handleSubmit = (e: React.FormEvent) => {
     e.preventDefault();
-    login({ email, password });
+    login({ email, password, rememberMe });
   };
 
   return (
@@ -54,6 +55,23 @@ export default function LoginPage() {
           />
         </div>
 
+        <div className="space-y-1">
+          <label className="flex cursor-pointer items-center gap-2">
+            <input
+              type="checkbox"
+              checked={rememberMe}
+              onChange={(e) => setRememberMe(e.target.checked)}
+              className="h-3.5 w-3.5 rounded border-zinc-600 bg-zinc-900 accent-white"
+            />
+            <span className="text-xs text-zinc-400">Remember me</span>
+          </label>
+          {rememberMe && (
+            <p className="pl-5 text-xs text-amber-500/80">
+              A refresh token will be stored locally — don&apos;t share it.
+            </p>
+          )}
+        </div>
+
         {error && <p className="text-xs text-red-400">{error.message}</p>}
 
         <button