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/platform/hooks/useBackButton.ts

@@ -1,53 +0,0 @@
-interface UseBackButtonOptions {
-  /**
-   * Whether the back button should be visible
-   * @default true
-   */
-  visible?: boolean;
-}
-
-/**
- * Hook to manage the Telegram BackButton
- *
- * NOTE: This hook is now a no-op for backward compatibility.
- * The Telegram Navigator (@telegram-apps/react-router-integration) handles
- * BackButton visibility and navigation automatically based on router history.
- *
- * The navigator:
- * - Shows BackButton when there's navigation history
- * - Hides BackButton on root page
- * - Handles back button clicks automatically
- *
- * @param onBack - (Ignored) Callback when back button is pressed
- * @param options - (Ignored) Configuration options
- *
- * @example
- * ```tsx
- * function MyPage() {
- *   const navigate = useNavigate();
- *   useBackButton(() => navigate('/admin')); // No-op: navigator handles this
- *   // ...
- * }
- * ```
- */
-export function useBackButton(
-  _onBack: (() => void) | null | undefined,
-  _options: UseBackButtonOptions = {},
-): void {
-  // No-op: Navigator handles BackButton automatically
-  return;
-}
-
-/**
- * Hook to conditionally show back button based on navigation depth
- *
- * NOTE: This hook is now a no-op for backward compatibility.
- * The navigator handles conditional visibility automatically.
- *
- * @param canGoBack - (Ignored) Whether navigation back is possible
- * @param onBack - (Ignored) Callback when back button is pressed
- */
-export function useConditionalBackButton(_canGoBack: boolean, _onBack: () => void): void {
-  // No-op: Navigator handles BackButton automatically
-  return;
-}