fix: Date picker bug

backend/src/core/config/database.ts

@@ -2,10 +2,15 @@
  * @ai-summary PostgreSQL connection pool configuration
  * @ai-context Shared pool for all feature repositories
  */
-import { Pool } from 'pg';
+import { Pool, types } from 'pg';
 import { logger } from '../logging/logger';
 import { appConfig } from './config-loader';
 
+// Override DATE type parser to return plain YYYY-MM-DD strings instead of Date objects.
+// Default pg behavior creates Date objects at local midnight, which shift dates when
+// serialized to JSON via toISOString() (UTC conversion) for clients in other timezones.
+types.setTypeParser(1082, (val: string) => val);
+
 export const pool = new Pool({
   connectionString: appConfig.getDatabaseUrl(),
   max: 10,

frontend/src/features/maintenance/components/MaintenanceRecordEditDialog.tsx

@@ -335,7 +335,7 @@ export const MaintenanceRecordEditDialog: React.FC<MaintenanceRecordEditDialogPr
               <Grid item xs={12} sm={6}>
                 <DatePicker
                   label="Service Date *"
-                  value={formData.date ? dayjs(formData.date) : null}
+                  value={formData.date ? dayjs(String(formData.date).substring(0, 10)) : null}
                   onChange={(newValue) =>
                     handleInputChange('date', newValue?.format('YYYY-MM-DD') || '')
                   }

frontend/src/features/maintenance/components/MaintenanceScheduleEditDialog.tsx

@@ -335,7 +335,7 @@ export const MaintenanceScheduleEditDialog: React.FC<MaintenanceScheduleEditDial
                 <Grid item xs={12}>
                   <DatePicker
                     label="Due Date"
-                    value={formData.fixedDueDate ? dayjs(formData.fixedDueDate) : null}
+                    value={formData.fixedDueDate ? dayjs(String(formData.fixedDueDate).substring(0, 10)) : null}
                     onChange={(newValue) =>
                       handleInputChange('fixedDueDate', newValue?.format('YYYY-MM-DD') || undefined)
                     }