fix: replace new Date() with dayjs for DATE column display and sorting (refs #237)

new Date("YYYY-MM-DD") parses as UTC midnight per ES2015. toLocaleDateString()
then displays in local time, shifting the date back one day for users west of
UTC. This caused the list view and edit dialog to show different dates.

Fixed in: MaintenanceRecordsList (display + sort + delete confirm),
VehicleDetailPage (display + sort), VehicleDetailMobile (display + sort),
MaintenanceRecordForm (receipt title), OwnershipCostsList (formatDate).

Sorting now uses string comparison (YYYY-MM-DD is lexicographically sortable).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/features/vehicles/mobile/VehicleDetailMobile.tsx

@@ -3,6 +3,7 @@
  */
 
 import React, { useMemo, useState } from 'react';
+import dayjs from 'dayjs';
 import { Box, Typography, Button, Card, CardContent, Divider, FormControl, InputLabel, Select, MenuItem, List, ListItem, ListItemButton, Dialog, DialogTitle, DialogContent } from '@mui/material';
 import { useQueryClient } from '@tanstack/react-query';
 import { Vehicle } from '../types/vehicles.types';
@@ -123,7 +124,7 @@ export const VehicleDetailMobile: React.FC<VehicleDetailMobileProps> = ({
         });
       }
     }
-    return list.sort((a, b) => new Date(b.date).getTime() - new Date(a.date).getTime());
+    return list.sort((a, b) => b.date.localeCompare(a.date));
   }, [fuelLogs]);
 
   const filteredRecords = useMemo(() => {
@@ -286,7 +287,7 @@ export const VehicleDetailMobile: React.FC<VehicleDetailMobileProps> = ({
                         </Box>
                         {/* Secondary line: Grade • Date • Type */}
                         <Typography variant="body2" color="text.secondary" sx={{ mt: 0.25 }}>
-                          {rec.secondary || `${new Date(rec.date).toLocaleDateString()} • ${rec.type}`}
+                          {rec.secondary || `${dayjs(rec.date).format('M/D/YYYY')} • ${rec.type}`}
                         </Typography>
                       </Box>
                     </ListItemButton>