Implement Scrabble move generator (DAWG) with English and Russian rules

A Go library that returns every legal play ranked by score and scores or
validates plays, using the Appel-Jacobson DAWG algorithm over
github.com/iliadenisov/dafsa v1.1.0.

- DAWG move generation (across / down / both), full tournament scoring with a
  per-tile breakdown; public Solver: GenerateMoves (ranked), ScorePlay,
  ValidatePlay.
- Rulesets: English Scrabble, Russian Scrabble, Эрудит (parameterizable Ruleset).
- cmd/builddict (build the DAWG from the dictionaries submodule), cmd/stress
  (self-play benchmark), selfplay engine; brute-force test oracle.
- A GADDAG was implemented, benchmarked and removed (the DAWG was smaller and
  faster for a scoring solver); see RESULTS.md and ALGORITHM.md.

scrabble/generator.go

@@ -0,0 +1,18 @@
+package scrabble
+
+import (
+	"scrabble-solver/board"
+	"scrabble-solver/rack"
+)
+
+// Generator produces every legal play for a position. The DAWG generator
+// (Appel-Jacobson) is the implementation; the interface keeps the self-play engine and
+// the solver decoupled from the concrete type.
+type Generator interface {
+	// GenerateMoves returns every legal play for rack r on board b in the modes'
+	// orientations. The result is unsorted; callers (or the Solver) rank it.
+	GenerateMoves(b *board.Board, r rack.Rack, mode Mode) []Move
+
+	// Name identifies the generator (e.g. "dawg").
+	Name() string
+}