fix(ui): default the profileless client to Erudit only, not every variant

availableVariants fell back to all three variants when the player had no
stored preferences. A fresh offline native launch boots with no profile, so
New Game exposed the English game before the player opted in — contrary to the
backend's Erudit-only new-account default (docs/FUNCTIONAL.md). Fall back to
DEFAULT_VARIANTS (Erudit only) instead; all dictionaries stay bundled.

ui/src/lib/variants.test.ts

@@ -2,6 +2,7 @@ import { describe, it, expect } from 'vitest';
 
 import {
   ALL_VARIANTS,
+  DEFAULT_VARIANTS,
   availableVariants,
   supportsMultipleWordsToggle,
   multipleWordsForRequest,
@@ -16,9 +17,11 @@ describe('ALL_VARIANTS', () => {
 });
 
 describe('availableVariants', () => {
-  it('is ungated (all variants) for an empty or absent preference set', () => {
-    expect(availableVariants([])).toEqual(ALL_VARIANTS);
-    expect(availableVariants(undefined)).toEqual(ALL_VARIANTS);
+  it('falls back to the Erudit-only default for an empty or absent preference set', () => {
+    const fallback = ALL_VARIANTS.filter((v) => DEFAULT_VARIANTS.includes(v.id));
+    expect(fallback.map((v) => v.id)).toEqual(['erudit_ru']);
+    expect(availableVariants([])).toEqual(fallback);
+    expect(availableVariants(undefined)).toEqual(fallback);
   });
 
   it('offers only the preferred variants', () => {