R1: schema & naming reset — squash migrations, rename variants

Squash the 12 goose migrations into one 00001_baseline.sql (there is no prod
data; verified schema-identical to the chain via a pg_dump diff + the green
integration suite) and rename the game-variant labels
english/russian_scrabble/erudit -> scrabble_en/scrabble_ru/erudit_ru across the
backend, the FlatBuffers wire values and the UI.

dawg filenames and the Go enum identifiers are unchanged; the i18n display keys
are kept. Adds PRERELEASE.md (the R1-R7 pre-release tracker), linked from
CLAUDE.md. Contour DB wipe and the scrabble-dictionary tidy are follow-ups.

backend/internal/robot/names_test.go

@@ -75,14 +75,14 @@ func TestPickVariantRouting(t *testing.T) {
 	s := &Service{poolEN: []uuid.UUID{enID}, poolRU: []uuid.UUID{ruID}}
 	for i := 0; i < 200; i++ {
 		if got, err := s.Pick(engine.VariantEnglish); err != nil || got != enID {
-			t.Fatalf("english Pick = (%v, %v), want (%v, nil)", got, err, enID)
+			t.Fatalf("scrabble_en Pick = (%v, %v), want (%v, nil)", got, err, enID)
 		}
 	}
 	var en, ru int
 	for i := 0; i < 4000; i++ {
 		got, err := s.Pick(engine.VariantRussianScrabble)
 		if err != nil {
-			t.Fatalf("russian Pick: %v", err)
+			t.Fatalf("scrabble_ru Pick: %v", err)
 		}
 		switch got {
 		case enID:
@@ -92,14 +92,14 @@ func TestPickVariantRouting(t *testing.T) {
 		}
 	}
 	if ru <= en {
-		t.Errorf("russian names should dominate a Russian game: ru=%d en=%d", ru, en)
+		t.Errorf("scrabble_ru names should dominate a Russian game: ru=%d en=%d", ru, en)
 	}
 	if en == 0 {
 		t.Errorf("some Latin names should appear in Russian games (got 0 of 4000)")
 	}
 	// Эрудит routes like Russian Scrabble.
 	if _, err := s.Pick(engine.VariantErudit); err != nil {
-		t.Errorf("erudit Pick: %v", err)
+		t.Errorf("erudit_ru Pick: %v", err)
 	}
 }
 
@@ -108,10 +108,10 @@ func TestPickVariantRouting(t *testing.T) {
 func TestPickFallback(t *testing.T) {
 	id := uuid.New()
 	if got, err := (&Service{poolEN: []uuid.UUID{id}}).Pick(engine.VariantRussianScrabble); err != nil || got != id {
-		t.Errorf("russian fallback to EN = (%v, %v), want (%v, nil)", got, err, id)
+		t.Errorf("scrabble_ru fallback to EN = (%v, %v), want (%v, nil)", got, err, id)
 	}
 	if got, err := (&Service{poolRU: []uuid.UUID{id}}).Pick(engine.VariantEnglish); err != nil || got != id {
-		t.Errorf("english fallback to RU = (%v, %v), want (%v, nil)", got, err, id)
+		t.Errorf("scrabble_en fallback to RU = (%v, %v), want (%v, nil)", got, err, id)
 	}
 	if _, err := (&Service{}).Pick(engine.VariantEnglish); !errors.Is(err, ErrNoRobotAvailable) {
 		t.Errorf("empty pool err = %v, want ErrNoRobotAvailable", err)