fix: display exact server error message on login failure

public/shell.php

@@ -159,7 +159,11 @@
                             navigate();
                         } catch (err) {
                             const errEl = document.getElementById('login-error');
-                            errEl.textContent = err.message || 'خطأ في الدخول';
+                            let msg = 'خطأ في الدخول';
+                            if (err && err.error && err.error.message_ar) msg = err.error.message_ar;
+                            else if (err && err.message) msg = err.message;
+                            else if (typeof err === 'string') msg = err;
+                            errEl.textContent = msg;
                             errEl.classList.remove('hidden');
                         }
                     };