feat(providers): add timestamp-based sorting for provider list

- Add createdAt timestamp field to Provider interface
- Implement sorting logic: old providers without timestamp first, then by creation time
- Providers without timestamps are sorted alphabetically by name
- New providers are automatically timestamped on creation

src/App.tsx

@@ -134,6 +134,7 @@ function App() {
     const newProvider: Provider = {
       ...provider,
       id: generateId(),
+      createdAt: Date.now(), // 添加创建时间戳
     };
     await window.api.addProvider(newProvider, activeApp);
     await loadProviders();