"Review changes" DML preview should be prettified and editable #25

The SQL shown in the "Review changes" dialog (before applying edits/deletes/inserts) is rendered as a cramped, wrapping, read-only block. It is hard to read and cannot be adjusted.

Requested

• Prettify the generated SQL (multi-line formatting).
• Make the SQL editable; when edited, run it as-is (raw statements) and refresh, while an unedited dialog keeps the safe structured per-cell writes.

Addressed by #21.