fix: use authenticated user ID for habit service

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/routes/(app)/habits/+page.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
 	import type { HabitWithCompletions } from '$lib/context/habits.svelte';
+	import type { User } from 'better-auth';
 	import HabitGrid from './HabitGrid.svelte';
 	import HabitCreationForm from './HabitCreationForm.svelte';
 	import { setHabitService } from '$lib/context/habits.svelte';
@@ -25,6 +26,8 @@
 	import { today, getLocalTimeZone } from '@internationalized/date';
 	import { onMount } from 'svelte';
 
+	let { data }: { data: { user: User } } = $props();
+
 	let showCreateDialog = $state(false);
 
 	// Date selection state
@@ -34,8 +37,9 @@
 	// Habit visibility toggle
 	let showInactiveHabits = $state(false);
 
-	// Create habit service instance - subscriptions will handle all data loading
-	const habitService = setHabitService('default-user');
+	// Create habit service instance with authenticated user
+	// svelte-ignore state_referenced_locally
+	const habitService = setHabitService(data.user!.id);
 
 	// Simple loading state - just show skeleton briefly while subscriptions initialize
 	let loading = $state(true);