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/premiums.test.ts

@@ -1,13 +1,13 @@
 import { describe, expect, it } from 'vitest';
 import { BOARD_SIZE, centre, premiumGrid } from './premiums';
 
-// Premium-square geometry parity with scrabble-solver/rules/rules.go: english/russian
-// share standardBoard (centre is a double word); erudit shares the geometry but a
+// Premium-square geometry parity with scrabble-solver/rules/rules.go: scrabble_en/scrabble_ru
+// share standardBoard (centre is a double word); erudit_ru shares the geometry but a
 // non-doubling centre. Tile-value and alphabet parity moved to the Go engine test
 // (backend/internal/engine AlphabetTable) in Stage 13 — the server now owns that table.
 describe('premium layout', () => {
   it('is a 15x15 grid with TW corners', () => {
-    const g = premiumGrid('english');
+    const g = premiumGrid('scrabble_en');
     expect(g.length).toBe(BOARD_SIZE);
     expect(g[0].length).toBe(BOARD_SIZE);
     for (const [r, c] of [
@@ -20,16 +20,16 @@ describe('premium layout', () => {
     }
   });
 
-  it('doubles the centre for standard variants but not for erudit', () => {
-    expect(centre('english')).toEqual({ row: 7, col: 7 });
-    expect(premiumGrid('english')[7][7]).toBe('DW');
-    expect(premiumGrid('russian_scrabble')[7][7]).toBe('DW');
-    expect(centre('erudit')).toEqual({ row: 7, col: 7 });
-    expect(premiumGrid('erudit')[7][7]).toBe('');
+  it('doubles the centre for standard variants but not for erudit_ru', () => {
+    expect(centre('scrabble_en')).toEqual({ row: 7, col: 7 });
+    expect(premiumGrid('scrabble_en')[7][7]).toBe('DW');
+    expect(premiumGrid('scrabble_ru')[7][7]).toBe('DW');
+    expect(centre('erudit_ru')).toEqual({ row: 7, col: 7 });
+    expect(premiumGrid('erudit_ru')[7][7]).toBe('');
   });
 
   it('keeps the standard premium counts', () => {
-    const flat = premiumGrid('english').flat();
+    const flat = premiumGrid('scrabble_en').flat();
     const count = (p: string) => flat.filter((x) => x === p).length;
     expect(count('TW')).toBe(8);
     expect(count('TL')).toBe(12);