Add screenshot of workflow manage TUI to Migration Assistant docs

[sumobrian]

Description

The Workflow CLI documentation for Migration Assistant 3.0 describes the workflow manage command as a terminal user interface (TUI), but doesn't include any visual showing what it looks like.

Adding a screenshot would help users understand what to expect when they run the command and make the documentation more approachable.

Location

• File: _migration-assistant/workflow-cli/index.md
• Section: "Use the workflow manage command as the primary interface"

Context

This was raised during tech review of PR #12302:
#12302 (comment)

Suggested improvement

Add a screenshot (or multiple) showing:

1. The workflow manage TUI main screen with migration phases visible
2. Optionally, an approval gate prompt

This would complement the existing text description:

workflow manage is a terminal user interface (TUI) — a full-screen interactive console that runs in your shell.