Progress bars / ETA for large-file CLI operations

[bytebrujo]

Problem

Spec §12.5 calls for progress bars with adaptive ETA, but they are not implemented.

Proposal

Show a progress bar with rolling-average ETA for long-running commands (convert, sort, query) on large files. Use the existing parser.stats (bytesProcessed/totalBytes/throughput). Only when stderr is a TTY.

Acceptance

• Progress bar on large-file ops when TTY
• Suppressed when piped / --quiet