Implement progressive enhancement for favorites button

- Add server-side form handling for favorites without JavaScript
- Create toggleFavorite server action that uses existing API endpoint
- Update FavoriteButton component with form-based fallback
- Maintain JavaScript enhancement for smoother UX when available
- Use server-side fetch to reuse centralized favorites API logic

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

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

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

@@ -1,6 +1,50 @@
-import { redirect } from '@sveltejs/kit';
+import { redirect, error } from '@sveltejs/kit';
 
 export const actions = {
+    toggleFavorite: async ({ request, locals, url, fetch }) => {
+        const session = await locals.auth();
+        
+        if (!session?.user?.nickname) {
+            throw error(401, 'Authentication required');
+        }
+        
+        const formData = await request.formData();
+        const recipeId = formData.get('recipeId') as string;
+        const isFavorite = formData.get('isFavorite') === 'true';
+        
+        if (!recipeId) {
+            throw error(400, 'Recipe ID required');
+        }
+        
+        try {
+            // Use the existing API endpoint
+            const method = isFavorite ? 'DELETE' : 'POST';
+            const response = await fetch('/api/rezepte/favorites', {
+                method,
+                headers: {
+                    'Content-Type': 'application/json',
+                },
+                body: JSON.stringify({ recipeId }),
+            });
+            
+            if (!response.ok) {
+                const errorData = await response.text();
+                console.error('API error:', response.status, errorData);
+                throw error(response.status, `Failed to toggle favorite: ${errorData}`);
+            }
+            
+            // Redirect back to the same page to refresh the state
+            throw redirect(303, url.pathname);
+        } catch (e) {
+            // If it's a redirect, let it through
+            if (e && typeof e === 'object' && 'status' in e && e.status === 303) {
+                throw e;
+            }
+            console.error('Favorite toggle error:', e);
+            throw error(500, 'Failed to toggle favorite');
+        }
+    },
+    
     swapYeast: async ({ request, url }) => {
         const formData = await request.formData();
         const yeastId = parseInt(formData.get('yeastId') as string);