feat(core): add allowGuestDemoWorkspace flag to force login (#12779)

https://github.com/user-attachments/assets/41a659c9-6def-4492-be8e-5910eb148d6f

This PR enforces login‑first access (#8716) by disabling or enabling the
guest demo workspace via Admin Server Client Page and redirecting
unauthenticated users straight to `/sign‑in`.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added a configuration option to control whether guest users can create
demo workspaces.
* Updated server and client interfaces, GraphQL schema, and queries to
support the new guest demo workspace flag.

* **Bug Fixes**
* Improved sign-out behavior to redirect users appropriately based on
guest demo workspace permissions.
* Enhanced navigation flow to handle guest demo workspace access and
user authentication state.

* **Tests**
* Added tests to verify sign-out logic when guest demo workspaces are
enabled or disabled.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: liuyi <forehalo@gmail.com>
Co-authored-by: fengmk2 <fengmk2@gmail.com>

packages/frontend/admin/src/config.json

@@ -190,6 +190,10 @@
     "earlyAccessControl": {
       "type": "Boolean",
       "desc": "Only allow users with early access features to access the app"
+    },
+    "allowGuestDemoWorkspace": {
+      "type": "Boolean",
+      "desc": "Whether allow guest users to create demo workspaces."
     }
   },
   "docService": {
@@ -207,6 +211,10 @@
     "versionControl.requiredVersion": {
       "type": "String",
       "desc": "Allowed version range of the app that allowed to access the server. Requires 'client/versionControl.enabled' to be true to take effect."
+    },
+    "allowGuestDemoWorkspace": {
+      "type": "Boolean",
+      "desc": "Allow guests to access demo workspace."
     }
   },
   "captcha": {