Desktop/remove hard requirement auth wall on desktop (#5956)

Co-authored-by: Claude Sonnet 4.6 <[email protected]>

frontend/src/desktop/components/SignInModal.tsx

@@ -0,0 +1,47 @@
+import { useEffect, useState } from 'react';
+import { Modal } from '@mantine/core';
+import { SetupWizard } from '@app/components/SetupWizard';
+import { OPEN_SIGN_IN_EVENT } from '@app/constants/signInEvents';
+import { Z_INDEX_SIGN_IN_MODAL } from '@app/styles/zIndex';
+
+export function SignInModal() {
+  const [opened, setOpened] = useState(false);
+  const [locked, setLocked] = useState(false);
+
+  useEffect(() => {
+    const handler = (e: Event) => {
+      const detail = (e as CustomEvent).detail;
+      setLocked(detail?.locked === true);
+      setOpened(true);
+    };
+    window.addEventListener(OPEN_SIGN_IN_EVENT, handler);
+    return () => window.removeEventListener(OPEN_SIGN_IN_EVENT, handler);
+  }, []);
+
+  if (!opened) return null;
+
+  return (
+    <Modal
+      opened={opened}
+      onClose={() => { if (!locked) setOpened(false); }}
+      size={520}
+      centered
+      withCloseButton={false}
+      closeOnClickOutside={!locked}
+      closeOnEscape={!locked}
+      padding={0}
+      radius="lg"
+      zIndex={Z_INDEX_SIGN_IN_MODAL}
+    >
+      <SetupWizard
+        noLayout
+        onClose={() => setOpened(false)}
+        onComplete={() => {
+          setOpened(false);
+          // No reload needed — AppProviders remounts the SaaS provider tree via
+          // connectionModeService subscription when mode changes.
+        }}
+      />
+    </Modal>
+  );
+}