Fix issue with QR code login and caching. Update README

src/static/app.js

@@ -215,15 +215,18 @@ document.getElementById("logout-btn").addEventListener("click", () => {
       headers: { "Content-Type": "application/json" },
       body: JSON.stringify({ code: k.toUpperCase() }),
     })
-      .then(res => res.ok ? res.json() : Promise.reject())
+      .then(res => res.ok ? res.json() : res.json().then(j => Promise.reject(j.detail || "Invalid keypass")))
       .then(data => {
         saveToken(data.token);
         showGatesView();
         loadGates();
       })
-      .catch(() => {
+      .catch(msg => {
         clearToken();
         showLogin();
+        const errEl = document.getElementById("login-error");
+        errEl.textContent = typeof msg === "string" ? msg : "QR code login failed";
+        errEl.classList.remove("hidden");
       });
     return;
   }