ADK web 2.0.0 offers Evals tab, but server reports 404

**Bug description**
ADK web UI provides an _Evals_ option, but this seems to fail.

**To reproduce**
Steps to reproduce the behavior:
1. Install `@google/adk@2.0.0` `@google/adk-devtools@2.0.0`
1. Run `adk web`
1. Open the web UI → _Evals_
1. Click _New_ or _Create Eval Set_ → choose a name → click _Create_
1. UI hangs while 404 is reported in the development tools console

**Expected behavior**
An eval-set gets created.

**Desktop:**
- OS: Fedora 44
- TS version/environment: 5.9.3
- ADK version: 2.0.0