Add a `word-provenance` command to `harper-cli` (and maybe a `just` command too)

A `harper-cli word-provenance` command would track whether a word is
- directly in the dictionary
- generated from a base word in the dictionary by its `/` annotation flags directly
- generated by the interaction of annotation flags and the `cross-product` property
- generated by the interaction of annotation flags on two entries that have the same letters but different letter cases (Harper's dictionary is case-folded internally).
- generated by any combination of the above, or generated via multiple routes.

For instance a word like "unboxing" might be generated from `unbox/G` and also from `boxing/U` and also from `unboxing/` directly.

See #3284 for a story of how unexpected spurious words can end up in Harper's dictionary and how they can trigger spurious lints - and how the causes can be unobvious and hard to discover.