Initial dictionary producer: builddict, word-list sources, DAWG build + CI

- builddict drives the de-internalized scrabble-solver dictdawg/wordlist builders
  (pinned v1.0.0) to produce the three DAWGs (en_sowpods, ru_scrabble, ru_erudit),
  byte-identical to the solver's committed fixtures (same dafsa/alphabet v1.1.0 -> no
  index drift with the running backend).
- Sources: english/sowpods.txt vendored from kamilmielnik/scrabble-dictionaries;
  russian/scrabble.txt + the dictprep tooling moved out of scrabble-solver.
- CI builds the DAWGs on push/PR and, on a vX.Y.Z tag, packages them flat into
  scrabble-dawg-<tag>.tar.gz and attaches it to the Gitea release.

.gitignore

@@ -0,0 +1,3 @@
+# Built DAWGs are release artifacts (published by CI on a vX.Y.Z tag), not committed.
+/dawg/
+/scrabble-dawg-*.tar.gz