feat(recipe): compress hero image to 400px preview on save

Adds Thumbnailator-based ImageCompressor that resizes uploaded images
to a 400px-wide JPEG preview stored in hero_image_preview. The recipe
list uses the preview instead of the full image URL.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/(app)/recipes/+page.server.ts

@@ -20,7 +20,7 @@ export const load: PageServerLoad = async ({ fetch }) => {
 					name: r.name!,
 					cookTimeMin: r.cookTimeMin,
 					effort: r.effort,
-					heroImageUrl: r.heroImageUrl
+					heroImagePreview: r.heroImagePreview
 				}));
 
 	const activePlan =