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

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 = [