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/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'
+        };
+    }
+};