Implement progressive enhancement for recipe multiplier with form fallbacks

Add form-based multiplier controls that work without JavaScript while providing enhanced UX when JS is available. Fixed fraction display and NaN flash issues.

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

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

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

@@ -1,6 +1,6 @@
 import { error } from "@sveltejs/kit";
 
-export async function load({ fetch, params}) {
+export async function load({ fetch, params, url}) {
     const res = await fetch(`/api/rezepte/items/${params.name}`);
     let item = await res.json();
     if(!res.ok){
@@ -19,8 +19,12 @@ export async function load({ fetch, params}) {
         // Silently fail if not authenticated or other error
     }
     
+    // Get multiplier from URL parameters
+    const multiplier = parseFloat(url.searchParams.get('multiplier') || '1');
+    
     return {
         ...item,
-        isFavorite
+        isFavorite,
+        multiplier
     };
 }