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.

ui/src/lib/variants.test.ts

@@ -9,14 +9,14 @@ describe('availableVariants', () => {
   });
 
   it('offers only English for an en-only service', () => {
-    expect(availableVariants(['en']).map((v) => v.id)).toEqual(['english']);
+    expect(availableVariants(['en']).map((v) => v.id)).toEqual(['scrabble_en']);
   });
 
   it('offers Russian and Эрудит for a ru-only service', () => {
-    expect(availableVariants(['ru']).map((v) => v.id)).toEqual(['russian_scrabble', 'erudit']);
+    expect(availableVariants(['ru']).map((v) => v.id)).toEqual(['scrabble_ru', 'erudit_ru']);
   });
 
   it('offers every variant for a bilingual service', () => {
-    expect(availableVariants(['en', 'ru']).map((v) => v.id)).toEqual(['english', 'russian_scrabble', 'erudit']);
+    expect(availableVariants(['en', 'ru']).map((v) => v.id)).toEqual(['scrabble_en', 'scrabble_ru', 'erudit_ru']);
   });
 });