TUI: Align enrollment with decision tree philosophy

[dkontango]

Update CLI TUI to match join webpage enrollment experience.

The join webpage implements the decision tree:

1. Machine identity (auto or custom)
2. Optional fields (user chooses what to expose)
3. Credentials (pre-provisioned access)

Both simple and advanced flows produce identical payloads.

CLI TUI should provide:

Interactive Mode (kontango enroll)

• Offer skill-level selection at start (optional)
• Interactive dialogs for each choice
• Show disclosure before enrollment
• Display payload before sending
• Pause for confirmation

Non-Interactive Mode (--no-tui)

• Show disclosure automatically
• Accept flags for all choices
• Clear about what will be sent
• Pause for user confirmation
• Provide enrollment code at end

Acceptance Criteria:

• TUI mirrors web decision tree exactly
• Same optional fields available in both
• Disclosure shown in both paths
• User can review full payload before sending
• Same SDK payload produced regardless of entry point

See: WEB_ENROLLMENT.md for the web implementation reference