DateTimeStep: swap date TextField to Input atom for consistency

- Preferred date fields now use Input atom (external label) instead of MUI TextField
- Removed unused TextField import
- Matches the name field pattern from session 30b

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

src/components/pages/DateTimeStep/DateTimeStep.tsx

@@ -1,6 +1,5 @@
 import React from 'react';
 import Box from '@mui/material/Box';
-import TextField from '@mui/material/TextField';
 import FormControl from '@mui/material/FormControl';
 import FormLabel from '@mui/material/FormLabel';
 import FormControlLabel from '@mui/material/FormControlLabel';
@@ -275,14 +274,13 @@ export const DateTimeStep: React.FC<DateTimeStepProps> = ({
               <Box sx={{ display: 'flex', flexDirection: 'column', gap: 2, mb: 3, pl: 4 }}>
                 {values.preferredDates.map((date, index) => (
                   <Box key={index} sx={{ display: 'flex', alignItems: 'flex-start', gap: 1 }}>
-                    <TextField
+                    <Input
                       label={DATE_LABELS[index] ?? `Preference ${index + 1}`}
                       type="date"
                       value={date}
                       onChange={(e) => handleDateChange(index, e.target.value)}
                       error={index === 0 && !!errors?.preferredDates}
                       helperText={index === 0 ? errors?.preferredDates : undefined}
-                      InputLabelProps={{ shrink: true }}
                       inputProps={{ min: minDate }}
                       fullWidth
                       required={index === 0}