fix: 下架后卡片变灰+按钮变灰，isActive存为boolean

根因: oils store 存 isActive = oil.is_active ?? true
  oil.is_active=0 时 0??true=0，但检查用 ===false，0!==false

修复: isActive = oil.is_active !== 0 (true/false boolean)

UI:
- 下架后弹窗不关闭，按钮变灰显示"✓ 已下架 · 点击重新上架"
- 卡片立即变灰(oil-chip--inactive class生效)
- 重新上架后恢复正常

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

frontend/src/stores/oils.js

@@ -68,7 +68,7 @@ export const useOilsStore = defineStore('oils', () => {
         bottlePrice: oil.bottle_price,
         dropCount: oil.drop_count,
         retailPrice: oil.retail_price ?? null,
-        isActive: oil.is_active ?? true,
+        isActive: oil.is_active !== 0,
         enName: oil.en_name ?? null,
       }
     }