[FEATURE] Move cursor up one line after Ctrl+U clears current line

Problem

When using Ctrl+U to clear the current line in the multi-line input, the cursor stays on the now-empty line. To clear multiple lines rapidly, you have to manually move up after each Ctrl+U. This adds friction when editing multi-line prompts.

Proposed solution

After Ctrl+U clears the current line, automatically move the cursor up to the previous line (if one exists). This allows rapidly clearing multiple lines by repeatedly pressing Ctrl+U without needing to manually navigate.

Codex CLI already implements this behavior, making it a proven UX pattern for CLI input editors.

Alternatives considered

• Manually pressing Up arrow after each Ctrl+U (current workaround)
• Selecting multiple lines and deleting (not always available in CLI input)

Priority

Medium

Category

Interactive mode (TUI)