13 matrix cells for the `explain` prefix across all three
wrapped commands — `explain show data` / `explain update` /
`explain delete` — covering each typing position (after the
prefix, the inner entry word, the table, the filter clause)
plus the three complete forms. The cells confirm `explain`
plugs into the inner query grammars cleanly: candidates, hints
and column scoping match the standalone commands, and the
complete forms parse as `Command::Explain`.
Also adds a worker test pinning the display SQL's `<>`
rendering of inequality (ADR-0028 §3).
Matrix: 161 -> 174 cells. 1172 tests pass; clippy clean.
claude@clouddev1