build-dictionary gains a --words mode that reads a plain list instead of the
upstream database. Everything after that — filtering, alias generation, writing
and verification — is the code the real build uses, so a fixture cannot drift
into being shaped differently from what the server loads.
testdata/fixture-words.txt is hand-written rather than extracted, so no test
artifact carries the upstream release's licence. Its graph is built around one
hub syllable: it is the only one with enough continuations for the server to
open a game on, so every game starts on a word ending in it and a scripted test
always knows the first answer.
