fix(web): export showAuthScreen to window so topbar Login works

The Login button (onclick=window.showAuthScreen()) was dead — showAuthScreen
was defined but never exported via Object.assign. Also drop dead code from
the e2e suite (unused createReadStream import, unused s3StreamRequest).

src/interfaces/http/controllers/home.html

@@ -363,7 +363,7 @@
     const init=async()=>{await checkAuth();await loadBuckets();};
     document.getElementById('authLoginBtn').addEventListener('click',handleLogin);
     document.getElementById('authTokenInput').addEventListener('keydown',e=>{if(e.key==='Enter')handleLogin();});
-    Object.assign(window, { switchBucket, navigateTo, debouncedSearch, downloadObject, copyLink, deleteObject, closeModal, showCreateBucketModal, createBucket, showCredentialsModal, logout });
+    Object.assign(window, { switchBucket, navigateTo, debouncedSearch, downloadObject, copyLink, deleteObject, closeModal, showCreateBucketModal, createBucket, showCredentialsModal, showAuthScreen, logout });
     init();
   </script>
 </body>