feat(items): add food category to item usage options

Update items table CHECK constraint to allow 'food' usage_key
Add 'food' to itemUsageOptions in backend queries with translations
Update design documentation to include the new category

DESIGN.md

@@ -663,6 +663,7 @@ Pokemon 详情页展示：
   - Relaxation
   - Toy
   - Road
+  - Food
 - 入手方式：可多选
 - 客制化：
   - 染色能力：`dyeability`，使用互斥枚举值维护：

backend/db/schema.sql

@@ -1214,7 +1214,7 @@ CREATE TABLE IF NOT EXISTS items (
     ancient_artifact_category_key IS NULL
     OR ancient_artifact_category_key IN ('lost-relics-l', 'lost-relics-s', 'fossils')
   ),
-  CHECK (usage_key IS NULL OR usage_key IN ('decoration', 'relaxation', 'toy', 'road'))
+  CHECK (usage_key IS NULL OR usage_key IN ('decoration', 'relaxation', 'toy', 'road', 'food'))
 );
 
 CREATE TABLE IF NOT EXISTS recipes (

backend/src/queries.ts

@@ -718,7 +718,8 @@ const itemUsageOptions = [
   { id: 1, key: 'decoration', labels: { en: 'Decoration', 'zh-CN': '装饰' } },
   { id: 2, key: 'relaxation', labels: { en: 'Relaxation', 'zh-CN': '休闲' } },
   { id: 3, key: 'toy', labels: { en: 'Toy', 'zh-CN': '玩具' } },
-  { id: 4, key: 'road', labels: { en: 'Road', 'zh-CN': '道路' } }
+  { id: 4, key: 'road', labels: { en: 'Road', 'zh-CN': '道路' } },
+  { id: 5, key: 'food', labels: { en: 'Food', 'zh-CN': '食物' } }
 ] as const satisfies readonly SystemListOption[];
 
 const ancientArtifactCategoryOptions = [