Add DateTimeStep page (wizard step 6)

- Centered-form layout with two fieldset sections: name + scheduling
- Grief-sensitive labels: "Their first name", "About the person who died"
- Pre-planning variant: softer copy, "About the person" (no "who died")
- Date preference: ASAP / specific with progressive disclosure date picker
- Time preference: 5-option radio (no preference, morning, midday, afternoon, evening)
- Religion/service style: Autocomplete with 22 options
- Save-and-exit tertiary CTA
- showNameFields + showScheduling props for conditional visibility per funeral type

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

src/components/pages/DateTimeStep/index.ts

@@ -0,0 +1,8 @@
+export { DateTimeStep, default } from './DateTimeStep';
+export type {
+  DateTimeStepProps,
+  DateTimeStepValues,
+  DateTimeStepErrors,
+  FuneralDatePref,
+  FuneralTimePref,
+} from './DateTimeStep';