Test: V2 workspace and model onboarding

Refs: #336779

- [ ] anyOS
- [ ] anyOS

Complexity: 2

Authors: @benibenj

---

Test the new two-step onboarding in the Agents Window. Focus on whether it behaves as expected and feels clear and smooth, rather than exhaustively testing every picker option.

## Set up

1. Use a build containing #336779 (a PR build, or Insiders after it lands).
2. Launch with **`--transient`** for temporary user data and extensions, for example:
```sh
code-insiders --transient --agents
```
Complete sign-in/setup and wait for an agent to be available.
3. In this window's user settings, enable the V2 developer preview:
```json
{
"onboarding.enabled": true,
"onboarding.developerMode": {
"sessions.onboarding.newSessionViewV2": true
},
"onboarding.developerModeVariations": {
"sessions.onboarding.newSessionViewV2": "workspaceAndModel"
}
}
```
4. Close Settings and return to **New Session**. **You may need to run Developer: Reload Window** for the tour to appear. It runs once per window load; reload to replay. A new `--transient` launch starts fresh, so reapply the settings and sign in again if necessary.

## Test

Try the flow both **without a workspace** and **with a workspace already selected** (select one, remain in New Session, and reload).

- The workspace picker is highlighted in both cases. It expands automatically only when no workspace is selected.
- You can press **Next** without choosing a workspace. On a replay, choose/change a workspace and verify the tour advances automatically after acceptance. Reselecting the same workspace should work too.
- There is **no harness spotlight**. The next step highlights the **model picker without expanding it**; you can still open it yourself and change models.
- Finish the tour and send a simple prompt, including a run without a workspace.

Try an untrusted local folder and leave its trust prompt open for a few seconds before accepting: the model step should still appear afterward. Declining trust must not incorrectly auto-advance.

Explore **Back, Next, Done, Skip/Escape**, and keyboard navigation. Check that highlights, picker popups, and focus behave sensibly and that no overlay blocks the composer after dismissal.

For a quick regression check, change the variation to `"default"` and reload: the workspace/harness/model tour should still work, with workspace selection optional. Report confusing copy or awkward transitions as well as functional bugs.

Start with a build containing #336779, launch it with `--transient --agents`, enable the listed onboarding settings, and open New Session. Exercise the workspace and model tour with and without a workspace, including trust, keyboard, replay, and default-variation cases. Done means confirming the flow, focus, highlights, dismissal, and prompt submission behave as described, while reporting functional bugs or confusing copy.

Written by the indexing model from the issue text.