fix partial field translation overwriting entire translation

When re-translating only changed fields (e.g., just ingredients), the partial
result was replacing the entire English translation, causing name, short_name,
description, and category to be lost.

Now merge partial translations with existing translation data to preserve
unchanged fields while updating only the modified ones.

src/lib/components/TranslationApproval.svelte

@@ -44,7 +44,15 @@
 			}
 
 			const result = await response.json();
+
+			// If translating only specific fields, merge with existing translation
+			// Otherwise use the full translation result
+			if (isEditMode && changedFields.length > 0 && englishData) {
+				editableEnglish = { ...englishData, ...result.translatedRecipe };
+			} else {
 				editableEnglish = result.translatedRecipe;
+			}
+
 			translationState = 'preview';
 
 			// Notify parent component