refactor: full codebase cleanup, dependency updates, and lint fixes

Phase 0: Remove ~920 lines of dead code (ThemeBentoPicker, PromoDiscountBadge,
AdminLayout, SettingsSidebar, MovingGradient, EmptyState, miniapp API, unused
types/functions/transitions/skeleton helpers). Fix API barrel file (add 20 missing exports).

Phase 1: Add ErrorBoundary (app/page/widget levels), centralize constants,
add axios timeout, fix staleTime:0 in React Query.

Phase 2: Consolidate hexToHsl, extract email validation, fix duplicate code.

Phase 3: Fix auth race condition (await checkAdminStatus), memoize useCurrency,
add WebSocket message validation.

Phase 4: Extract useBranding, useFeatureFlags, useScrollRestoration from AppShell.

Phase 5: Remove all eslint-disable react-hooks/exhaustive-deps (14 total),
simplify logger, remove deprecated hooks (useBackButton, useTelegramDnd,
useTelegramWebApp).

Dependencies: React 19, react-router 7, zustand 5, i18next 25, react-i18next 16,
eslint-plugin-react-refresh 0.5. Remove unused @lottiefiles/dotlottie-react.
Convert vite manualChunks to function-based approach for react-router v7 compat.

Lint: Fix logger.ts no-unused-expressions, fix react-refresh/only-export-components
in 6 Radix primitive files (const re-exports → direct re-exports), fix
WebSocketProvider exhaustive-deps. Result: 0 errors, 0 warnings.

Add CLAUDE.md to .gitignore.

src/hooks/useFeatureFlags.ts

@@ -0,0 +1,49 @@
+import { useQuery } from '@tanstack/react-query';
+import { useAuthStore } from '@/store/auth';
+import { referralApi } from '@/api/referral';
+import { wheelApi } from '@/api/wheel';
+import { contestsApi } from '@/api/contests';
+import { pollsApi } from '@/api/polls';
+
+export function useFeatureFlags() {
+  const { isAuthenticated } = useAuthStore();
+
+  const { data: referralTerms } = useQuery({
+    queryKey: ['referral-terms'],
+    queryFn: referralApi.getReferralTerms,
+    enabled: isAuthenticated,
+    staleTime: 60000,
+    retry: false,
+  });
+
+  const { data: wheelConfig } = useQuery({
+    queryKey: ['wheel-config'],
+    queryFn: wheelApi.getConfig,
+    enabled: isAuthenticated,
+    staleTime: 60000,
+    retry: false,
+  });
+
+  const { data: contestsCount } = useQuery({
+    queryKey: ['contests-count'],
+    queryFn: contestsApi.getCount,
+    enabled: isAuthenticated,
+    staleTime: 60000,
+    retry: false,
+  });
+
+  const { data: pollsCount } = useQuery({
+    queryKey: ['polls-count'],
+    queryFn: pollsApi.getCount,
+    enabled: isAuthenticated,
+    staleTime: 60000,
+    retry: false,
+  });
+
+  return {
+    referralEnabled: referralTerms?.is_enabled,
+    wheelEnabled: wheelConfig?.is_enabled,
+    hasContests: (contestsCount?.count ?? 0) > 0,
+    hasPolls: (pollsCount?.count ?? 0) > 0,
+  };
+}