tui: fix approval dialog for large commands

[nornagon-openai]

Summary

• Emit a “Proposed Command” history cell when an ExecApprovalRequest arrives (parity with proposed patches).
• Simplify the approval dialog: show only the reason/instructions; move the command preview into history.
• Make approval/abort decision history concise:
  • Single line snippet; if multiline, show first line + " ...".
  • Truncate to 80 graphemes with ellipsis for very long commands.

Details

• History
  • Add new_proposed_command to render a header and indented command preview.
  • Use shared prefix_lines helper for first/subsequent line prefixes.
• Approval UI
  • UserApprovalWidget no longer renders the command in the modal; shows optional reason text only.
  • Decision history renders an inline, dimmed snippet per rules above.
• Tests (snapshot-based)
  • Proposed/decision flow for short command.
  • Proposed multi-line + aborted decision snippet with “ ...”.
  • Very long one-line command -> truncated snippet with “…”.
  • Updated existing exec approval snapshots and test reasons.

after approving:

rejection:

big command:

Screen.Recording.2025-09-03.at.12.04.27.PM.mov