Fixed warnings from svelte about mutability

src/routes/private/events/event/new/components/EmailSettingsStep.svelte

@@ -1,5 +1,5 @@
 <script lang="ts">
-	let { emailData, errors } = $props<{
+	let { emailData = $bindable(), errors = $bindable() } = $props<{
 		emailData: {
 			subject: string;
 			body: string;

src/routes/private/events/event/new/components/EventDetailsStep.svelte

@@ -1,5 +1,5 @@
 <script lang="ts">
-	let { eventData, errors } = $props<{
+	let { eventData = $bindable(), errors = $bindable() } = $props<{
 		eventData: {
 			name: string;
 			date: string;

src/routes/private/events/event/new/components/GoogleSheetsStep.svelte

@@ -2,7 +2,7 @@
 	import type { GoogleSheet } from '$lib/google/sheets/types.ts';
 	
 	// Props
-	let { sheetsData, errors, loadRecentSheets, selectSheet, toggleSheetList } = $props<{
+	let { sheetsData = $bindable(), errors = $bindable(), loadRecentSheets, selectSheet, toggleSheetList } = $props<{
 		sheetsData: {
 			availableSheets: GoogleSheet[];
 			selectedSheet: GoogleSheet | null;