fix: before admin stations removal

frontend/src/features/settings/api/preferences.api.ts

@@ -0,0 +1,13 @@
+/**
+ * @ai-summary API client for user preferences endpoints
+ * @ai-context Handles unit system, currency, and timezone preferences sync
+ */
+
+import { apiClient } from '../../../core/api/client';
+import { UserPreferences, UpdatePreferencesRequest } from '../types/preferences.types';
+
+export const preferencesApi = {
+  getPreferences: () => apiClient.get<UserPreferences>('/user/preferences'),
+  updatePreferences: (data: UpdatePreferencesRequest) =>
+    apiClient.put<UserPreferences>('/user/preferences', data),
+};

frontend/src/features/settings/hooks/usePreferences.ts

@@ -0,0 +1,61 @@
+/**
+ * @ai-summary React hooks for user preferences management
+ * @ai-context Handles unit system, currency, and timezone preference sync with backend
+ */
+
+import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
+import { useAuth0 } from '@auth0/auth0-react';
+import { preferencesApi } from '../api/preferences.api';
+import { UpdatePreferencesRequest } from '../types/preferences.types';
+import toast from 'react-hot-toast';
+
+interface ApiError {
+  response?: {
+    data?: {
+      error?: string;
+      message?: string;
+    };
+  };
+  message?: string;
+}
+
+export const usePreferences = () => {
+  const { isAuthenticated, isLoading } = useAuth0();
+
+  return useQuery({
+    queryKey: ['user-preferences'],
+    queryFn: async () => {
+      const response = await preferencesApi.getPreferences();
+      return response.data;
+    },
+    enabled: isAuthenticated && !isLoading,
+    staleTime: 5 * 60 * 1000, // 5 minutes
+    gcTime: 10 * 60 * 1000, // 10 minutes cache time
+    retry: (failureCount, error: any) => {
+      // Retry 401s a few times (auth token might be refreshing)
+      if (error?.response?.status === 401 && failureCount < 3) {
+        return true;
+      }
+      return false;
+    },
+    retryDelay: (attemptIndex) => Math.min(1000 * 2 ** attemptIndex, 30000),
+    refetchOnWindowFocus: false,
+    refetchOnMount: false,
+  });
+};
+
+export const useUpdatePreferences = () => {
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: (data: UpdatePreferencesRequest) => preferencesApi.updatePreferences(data),
+    onSuccess: (response) => {
+      queryClient.setQueryData(['user-preferences'], response.data);
+      // Don't show toast for unit system changes - context handles UI feedback
+    },
+    onError: (error: ApiError) => {
+      const message = error.response?.data?.message || error.response?.data?.error || 'Failed to update preferences';
+      toast.error(message);
+    },
+  });
+};

frontend/src/features/settings/hooks/useSettings.ts

@@ -1,5 +1,6 @@
 import { useState, useEffect } from 'react';
 import { useSettingsPersistence, SettingsState } from './useSettingsPersistence';
+import { useUnits } from '../../../core/units/UnitsContext';
 
 const defaultSettings: SettingsState = {
   darkMode: false,
@@ -13,10 +14,12 @@ const defaultSettings: SettingsState = {
 
 export const useSettings = () => {
   const { loadSettings, saveSettings } = useSettingsPersistence();
+  const { unitSystem: contextUnitSystem, setUnitSystem: setContextUnitSystem } = useUnits();
   const [settings, setSettings] = useState<SettingsState>(defaultSettings);
   const [isLoading, setIsLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
 
+  // Load settings from localStorage on mount
   useEffect(() => {
     try {
       setIsLoading(true);
@@ -33,6 +36,13 @@ export const useSettings = () => {
     }
   }, [loadSettings]);
 
+  // Sync unitSystem from context (which may load from backend)
+  useEffect(() => {
+    if (contextUnitSystem && contextUnitSystem !== settings.unitSystem) {
+      setSettings(prev => ({ ...prev, unitSystem: contextUnitSystem }));
+    }
+  }, [contextUnitSystem, settings.unitSystem]);
+
   const updateSetting = <K extends keyof SettingsState>(
     key: K,
     value: SettingsState[K]
@@ -42,6 +52,11 @@ export const useSettings = () => {
       const newSettings = { ...settings, [key]: value };
       setSettings(newSettings);
       saveSettings(newSettings);
+
+      // Sync unitSystem changes to context (which syncs to backend)
+      if (key === 'unitSystem' && typeof value === 'string') {
+        setContextUnitSystem(value as 'imperial' | 'metric');
+      }
     } catch (err) {
       setError(err instanceof Error ? err.message : 'Failed to save settings');
     }

frontend/src/features/settings/mobile/MobileSettingsScreen.tsx

@@ -367,7 +367,7 @@ export const MobileSettingsScreen: React.FC = () => {
                 <div>
                   <p className="font-medium text-slate-800">Unit System</p>
                   <p className="text-sm text-slate-500">
-                    Currently using {settings.unitSystem === 'imperial' ? 'Miles & Gallons' : 'Kilometers & Liters'}
+                    Currently using {settings.unitSystem === 'imperial' ? 'Miles, Gallons, MPG, USD' : 'Km, Liters, L/100km, EUR'}
                   </p>
                 </div>
                 <button

frontend/src/features/settings/types/preferences.types.ts

@@ -0,0 +1,22 @@
+/**
+ * @ai-summary Type definitions for user preferences
+ * @ai-context Types for unit system, currency, and timezone preferences
+ */
+
+import { UnitSystem } from '../../../core/units/units.types';
+
+export interface UserPreferences {
+  id: string;
+  userId: string;
+  unitSystem: UnitSystem;
+  currencyCode: string;
+  timeZone: string;
+  createdAt: string;
+  updatedAt: string;
+}
+
+export interface UpdatePreferencesRequest {
+  unitSystem?: UnitSystem;
+  currencyCode?: string;
+  timeZone?: string;
+}