fix: reload dashboard under http node root

[Saithej2k]

Summary

• Build forced reload URLs from the dashboard base path instead of always using /dashboard.
• Use the _setup response URL when unauthenticated responses arrive before setup is stored.

Testing

• git diff --check
• node --check ui/src/main.mjs

Closes #2149

[colinl]

Is the change to use the setup url in the case of authentication error anything to do with issue #2149 or is that to address a different issue?

[Saithej2k]

Good point. I narrowed that part out so the auth path no longer depends on the _setup response URL. The reload URL now comes from the stored setup base path when available, or from the current dashboard path, which keeps the change focused on #2149.

[colinl]

While you have your brain in gear for the dashboard url, you might like to have a look at #2132.

Does the Open Dashboard button in the editor work if the root is altered?

[Saithej2k]

I checked both paths. The Open Dashboard button already prefixes the configured dashboard path with RED.settings.httpNodeRoot, so it produces the correct URL when the root is changed.

The #2132 failure is separate: the layout editor save request derived its API path from the dashboard URL and then prepended the editor path, which could duplicate the custom root. I fixed that path and added coverage for default, shared, and different admin/node roots in #2165. I kept this PR scoped to the forced-reload behavior from #2149.