[BUG] Can add users without selecting them in the Project/Namespaces `Add Project Member` dialog

[joesims22]

Setup

• Rancher version: v2.13.0-alpha3
• Browser type & version: Version 140.0.7339.186 (Official Build) (arm64)

Describe the bug
When accessing the Add Project Member dialog via creating a project or editing the config of an existing project it's possible to type a user in without selecting them and add them to the list of members without an error being thrown.
When trying to save the changes the error expected to be seen from the typed in user is thrown.

To Reproduce

1. In Rancher navigate to either the local/downstream cluster -> Project/Namespaces
2. Create a Project
3. Click Add to open the Add Project Member dialog
4. Type a non-existent user into the Select Member field and click Add
5. Observe the non-existent user is added to the project list instead of an error being thrown in the dialog
6. Attempt to save the changes and the expected error is thrown
7. Remove the non-existent user
8. Create a new project and save
9. In the Projects/Namespaces page select Edit Config for the new project
10. Click Add to open the Add Project Member dialog
11. Observe the non-existent user is added to the project list instead of an error being thrown in the dialog
12. Attempt to save the changes and the expected error is thrown.

Result

Expected Result

The Validation failed in API: must target a user [userId]/[userPrincipalId] OR a group [groupId]/[groupPrincipalId] error should be thrown inside the Add Project Member dialog box instead of adding the non-existent user to the list of members.

Similar to the behavior when accessing the Add Project Member dialog from the Clusters and Project Members page.

Screenshots

Screen.Recording.2025-10-24.at.2.14.08.PM.mov