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/lib/recipes/RecipeCard.svelte

@@ -23,8 +23,8 @@
 			data-testid="image-area"
 			class="w-full overflow-hidden {compact ? 'h-[64px]' : 'h-[100px]'}"
 		>
-			{#if recipe.heroImageUrl}
-				<img src={recipe.heroImageUrl} alt={recipe.name} class="w-full h-full object-cover" />
+			{#if recipe.heroImagePreview}
+				<img src={recipe.heroImagePreview} alt={recipe.name} class="w-full h-full object-cover" />
 			{:else}
 				<div
 					data-testid="image-placeholder"