Add row preview/selection aids for Keeper review

[rkboyce]

Title
Add row preview and operator-friendly row selection for ACP-based Keeper review

Body

Problem

Keeper review now supports explicit row selection and resume, but row choice is still effectively blind. There is no preview/listing helper to show available rows before selecting indices or ranges.

Current behavior

Users can enter row selections such as:

• 1-3,5
• all

But they do not get a concise row inventory to guide that choice.

Risk

• poor operator usability
• unnecessary reruns
• accidental review of the wrong rows

Requested change

Add a concise preview/listing layer before row selection.

Acceptance criteria

• users can see an inventory of generated rows before choosing indices
• preview avoids exposing more detail than intended for dialogue safety
• selection UX supports:
  • default first N
  • explicit ranges
  • all rows
• persisted state records the selected row subset
• tests cover row preview and selection parsing behavior