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/useScrollRestoration.ts

@@ -0,0 +1,40 @@
+import { useEffect, useRef } from 'react';
+import { useLocation } from 'react-router';
+
+/**
+ * Saves and restores scroll position for admin pages.
+ * Disables browser's automatic scroll restoration.
+ */
+export function useScrollRestoration() {
+  const location = useLocation();
+  const scrollPositions = useRef<Record<string, number>>({});
+
+  // Disable browser's automatic scroll restoration
+  useEffect(() => {
+    if ('scrollRestoration' in history) {
+      history.scrollRestoration = 'manual';
+    }
+  }, []);
+
+  // Save/restore scroll for admin pages
+  useEffect(() => {
+    const currentPath = location.pathname;
+
+    if (!currentPath.startsWith('/admin')) return;
+
+    const handleScroll = () => {
+      scrollPositions.current[currentPath] = window.scrollY;
+    };
+
+    window.addEventListener('scroll', handleScroll, { passive: true });
+
+    const savedPosition = scrollPositions.current[currentPath];
+    if (savedPosition !== undefined && savedPosition > 0) {
+      window.scrollTo({ top: savedPosition, behavior: 'instant' });
+    }
+
+    return () => {
+      window.removeEventListener('scroll', handleScroll);
+    };
+  }, [location.pathname]);
+}