feat: add provider duplicate functionality in edit mode

Add a duplicate button next to the drag handle in edit mode that allows users to quickly copy existing provider configurations.

- Add Copy icon button in ProviderCard next to drag handle
- Implement handleDuplicateProvider in App.tsx with deep cloning
- Copy all provider settings (settingsConfig, websiteUrl, category, meta)
- Auto-generate new ID and timestamp, omit sortIndex for natural sorting
- Append " copy" to duplicated provider name
- Add i18n support (zh: "复制", en: "Duplicate")
- Wire onDuplicate callback through ProviderList to ProviderCard

The duplicated provider will appear below the original provider in the list, sorted by creation time.

src/i18n/locales/zh.json

@@ -72,6 +72,7 @@
     "removeFromClaudePlugin": "从 Claude 插件移除",
     "dragToReorder": "拖拽以重新排序",
     "dragHandle": "拖拽排序",
+    "duplicate": "复制",
     "sortUpdateFailed": "排序更新失败",
     "configureUsage": "配置用量查询",
     "name": "供应商名称",