fix: 修改公共配方中文名时自动重新翻译英文名

改名但没手动指定英文名时，自动用 auto_translate 重新生成。

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/main.py

@@ -858,6 +858,9 @@ def update_recipe(recipe_id: int, update: RecipeUpdate, user=Depends(get_current
 
     if update.name is not None:
         c.execute("UPDATE recipes SET name = ? WHERE id = ?", (update.name, recipe_id))
+        # Re-translate en_name if name changed and no explicit en_name provided
+        if update.en_name is None:
+            c.execute("UPDATE recipes SET en_name = ? WHERE id = ?", (auto_translate(update.name), recipe_id))
     if update.note is not None:
         c.execute("UPDATE recipes SET note = ? WHERE id = ?", (update.note, recipe_id))
     if update.en_name is not None: