[All Platforms][Onboard][GitHub Issue #6005] nemoclaw onboard wizard has no back-navigation — users cannot correct a previous step without Ctrl+C #6005

Description

The nemoclaw onboard wizard is strictly forward-only. Once a user advances past a step (e.g., Brave Search API setup, provider selection, sandbox name entry), there is no way to go back and change it without pressing Ctrl+C — which users interpret as aborting the entire install rather than navigating back.

Request: add a back-navigation key (b or Backspace) at each wizard prompt that returns the user to the previous step and allows re-entry, without discarding progress made on later steps already completed.

Affects all platforms. Observed and reported across: DGX Station, macOS (Brev/Cursor), and DGX Station installer sub-flows.

Environment

• Device: All Platforms
• OS: All Platforms
• NemoClaw: v0.0.67+

Steps to Reproduce

1. Run nemoclaw onboard on any platform.
2. Advance past any wizard prompt (e.g., enter a sandbox name or provider selection).
3. At the next prompt, attempt to go back and change the previous answer.
4. Observe that no back-navigation option exists.

Expected Result

Each wizard prompt offers a visible back-navigation option (e.g., [b] Back). Pressing b or Backspace returns the user to the previous prompt with their prior answer pre-filled, allowing correction without restarting.

Actual Result

No back option exists. The only escape is Ctrl+C, which terminates the wizard entirely. Users who mistype a sandbox name or select the wrong provider must re-run the full onboard flow.