Implement user favorites feature for recipes

- Add UserFavorites MongoDB model with ObjectId references
- Create authenticated API endpoints for favorites management
- Add Heart icon and FavoriteButton components with toggle functionality
- Display favorite button below recipe tags for logged-in users
- Add Favoriten navigation link (visible only when authenticated)
- Create favorites page with grid layout and search functionality
- Store favorites by MongoDB ObjectId for data integrity

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/routes/rezepte/+layout.svelte

@@ -11,6 +11,9 @@ if(data.session){
 <Header>
 	<ul class=site_header slot=links>
 	<li><a href="/rezepte">Alle Rezepte</a></li>
+	{#if user}
+		<li><a href="/rezepte/favorites">Favoriten</a></li>
+	{/if}
 	<li><a href="/rezepte/season">In Saison</a></li>
 	<li><a href="/rezepte/category">Kategorie</a></li>
 	<li><a href="/rezepte/icon">Icon</a></li>

src/routes/rezepte/[name]/+page.svelte

@@ -12,6 +12,7 @@
     	import {season} from '$lib/js/season_store';
 	import RecipeNote from '$lib/components/RecipeNote.svelte';
 	import {stripHtmlTags} from '$lib/js/stripHtmlTags';
+	import FavoriteButton from '$lib/components/FavoriteButton.svelte';
 
     	export let data: PageData;
 
@@ -308,6 +309,15 @@ h4{
 				<a class=tag href="/rezepte/tag/{tag}">{tag}</a>
 			{/each}
 		</div>
+		
+		<div class="tags center">
+			<FavoriteButton 
+				recipeId={data.short_name} 
+				isFavorite={data.isFavorite || false} 
+				isLoggedIn={!!data.session?.user} 
+			/>
+		</div>
+		
 		{#if data.note}
 			<RecipeNote note={data.note}></RecipeNote>
 		{/if}

src/routes/rezepte/[name]/+page.ts

@@ -6,5 +6,21 @@ export async function load({ fetch, params}) {
     if(!res.ok){
 	    throw error(res.status, item.message)
     }
-    return item;
+    
+    // Check if this recipe is favorited by the user
+    let isFavorite = false;
+    try {
+        const favRes = await fetch(`/api/rezepte/favorites/check/${params.name}`);
+        if (favRes.ok) {
+            const favData = await favRes.json();
+            isFavorite = favData.isFavorite;
+        }
+    } catch (e) {
+        // Silently fail if not authenticated or other error
+    }
+    
+    return {
+        ...item,
+        isFavorite
+    };
 }

src/routes/rezepte/favorites/+page.server.ts

@@ -0,0 +1,32 @@
+import type { PageServerLoad } from "./$types";
+import { redirect } from '@sveltejs/kit';
+
+export const load: PageServerLoad = async ({ fetch, locals }) => {
+    const session = await locals.auth();
+    
+    if (!session?.user?.nickname) {
+        throw redirect(302, '/rezepte');
+    }
+
+    try {
+        const res = await fetch('/api/rezepte/favorites/recipes');
+        if (!res.ok) {
+            return {
+                favorites: [],
+                error: 'Failed to load favorites'
+            };
+        }
+        
+        const favorites = await res.json();
+        
+        return {
+            favorites,
+            session
+        };
+    } catch (e) {
+        return {
+            favorites: [],
+            error: 'Failed to load favorites'
+        };
+    }
+};

src/routes/rezepte/favorites/+page.svelte

@@ -0,0 +1,58 @@
+<script lang="ts">
+    import type { PageData } from './$types';
+    import '$lib/css/nordtheme.css';
+    import Recipes from '$lib/components/Recipes.svelte';
+    import Card from '$lib/components/Card.svelte';
+    import Search from '$lib/components/Search.svelte';
+    export let data: PageData;
+    export let current_month = new Date().getMonth() + 1;
+</script>
+
+<style>
+h1{
+    text-align: center;
+    margin-bottom: 0;
+    font-size: 4rem;
+}
+.subheading{
+    text-align: center;
+    margin-top: 0;
+    font-size: 1.5rem;
+}
+.empty-state{
+    text-align: center;
+    margin-top: 3rem;
+    color: var(--nord3);
+}
+</style>
+
+<svelte:head>
+    <title>Meine Favoriten - Bocken Rezepte</title>
+    <meta name="description" content="Meine favorisierten Rezepte aus der Bockenschen Küche." />
+</svelte:head>
+
+<h1>Favoriten</h1>
+<p class=subheading>
+    {#if data.favorites.length > 0}
+        {data.favorites.length} favorisierte Rezepte
+    {:else}
+        Noch keine Favoriten gespeichert
+    {/if}
+</p>
+
+<Search></Search>
+
+{#if data.error}
+    <p class="empty-state">Fehler beim Laden der Favoriten: {data.error}</p>
+{:else if data.favorites.length > 0}
+    <Recipes>
+        {#each data.favorites as recipe}
+            <Card {recipe} {current_month}></Card>
+        {/each}
+    </Recipes>
+{:else}
+    <div class="empty-state">
+        <p>Du hast noch keine Rezepte als Favoriten gespeichert.</p>
+        <p>Besuche ein <a href="/rezepte">Rezept</a> und klicke auf das Herz-Symbol, um es zu deinen Favoriten hinzuzufügen.</p>
+    </div>
+{/if}