Use headless terminal emulator (e.g., xterm.js) to handle progress bars and \r correctly

Problem

When running commands with progress bars or carriage return (\r) updates, Claude Code shows every single state instead of the final output. The \r characters are ignored rather than interpreted.

Example output from a 100-step progress bar:

Progress: [#   ] 1%Progress: [##  ] 2%Progress: [### ] 3%...Progress: [####] 100%

All 100 states are concatenated, consuming tokens unnecessarily.

Expected Behavior

Only the final state of each line should be captured, as it would appear in a real terminal.

Suggested Fix

Use a headless terminal emulator like xterm.js to properly interpret terminal control sequences (\r, ANSI escapes, etc.) before capturing output.