e2e: remove auth bypass; use real Clerk sign-in in Cypress

frontend/src/app/activity/page.tsx

@@ -302,7 +302,7 @@ export default function ActivityPage() {
               forceRedirectUrl="/activity"
               signUpForceRedirectUrl="/activity"
             >
-              <Button className="mt-4">Sign in</Button>
+              <Button className="mt-4" data-testid="activity-signin">Sign in</Button>
             </SignInButton>
           </div>
         </div>

frontend/src/auth/clerk.tsx

@@ -19,29 +19,20 @@ import type { ComponentProps } from "react";
 
 import { isLikelyValidClerkPublishableKey } from "@/auth/clerkKey";
 
-function isE2EAuthBypassEnabled(): boolean {
-  // Used only for Cypress E2E to keep tests secretless and deterministic.
-  // When enabled, we treat the user as signed in and skip Clerk entirely.
-  return process.env.NEXT_PUBLIC_E2E_AUTH_BYPASS === "1";
-}
-
 export function isClerkEnabled(): boolean {
   // IMPORTANT: keep this in sync with AuthProvider; otherwise components like
   // <SignedOut/> may render without a <ClerkProvider/> and crash during prerender.
-  if (isE2EAuthBypassEnabled()) return false;
   return isLikelyValidClerkPublishableKey(
     process.env.NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY,
   );
 }
 
 export function SignedIn(props: { children: ReactNode }) {
-  if (isE2EAuthBypassEnabled()) return <>{props.children}</>;
   if (!isClerkEnabled()) return null;
   return <ClerkSignedIn>{props.children}</ClerkSignedIn>;
 }
 
 export function SignedOut(props: { children: ReactNode }) {
-  if (isE2EAuthBypassEnabled()) return null;
   if (!isClerkEnabled()) return <>{props.children}</>;
   return <ClerkSignedOut>{props.children}</ClerkSignedOut>;
 }
@@ -67,15 +58,6 @@ export function useUser() {
 }
 
 export function useAuth() {
-  if (isE2EAuthBypassEnabled()) {
-    return {
-      isLoaded: true,
-      isSignedIn: true,
-      userId: "e2e-user",
-      sessionId: "e2e-session",
-      getToken: async () => "e2e-token",
-    } as const;
-  }
   if (!isClerkEnabled()) {
     return {
       isLoaded: true,