fix(auth): align alert live region semantics

ui/src/pages/Auth.test.tsx

@@ -188,7 +188,7 @@ describe("AuthPage", () => {
 
     const alert = container.querySelector('[role="alert"]') as HTMLElement;
     expect(alert).not.toBeNull();
-    expect(alert.getAttribute("aria-live")).toBe("polite");
+    expect(alert.hasAttribute("aria-live")).toBe(false);
     expect(alert.textContent).toContain("Invalid email or password");
 
     const errorId = alert.id;

ui/src/pages/Auth.tsx

@@ -158,7 +158,7 @@ export function AuthPage() {
               />
             </div>
             {error && (
-              <p id={errorId} role="alert" aria-live="polite" className="text-xs text-destructive">
+              <p id={errorId} role="alert" className="text-xs text-destructive">
                 {error}
               </p>
             )}

ui/src/pages/InviteLanding.test.tsx

@@ -320,7 +320,7 @@ describe("InviteLandingPage", () => {
 
     const alert = container.querySelector('[role="alert"]') as HTMLElement;
     expect(alert).not.toBeNull();
-    expect(alert.getAttribute("aria-live")).toBe("polite");
+    expect(alert.hasAttribute("aria-live")).toBe(false);
 
     const errorId = alert.id;
     expect(errorId.length).toBeGreaterThan(0);

ui/src/pages/InviteLanding.tsx

@@ -770,7 +770,6 @@ export function InviteLandingPage() {
                     <p
                       id={authErrorId}
                       role="alert"
-                      aria-live="polite"
                       className={`text-xs ${
                         authFeedback.tone === "info" ? "text-amber-300" : "text-red-400"
                       }`}