fix(desktop): ConfigMigrationWizard PUT 使用 config item ID 替代布尔值

M7-02: exists 是 boolean，不能用作 URL 路径参数。
改为使用 saasConfigs.find() 获取完整对象，
用 existing.id 作为 PUT 路径参数。

desktop/src/components/SaaS/ConfigMigrationWizard.tsx

@@ -102,8 +102,8 @@ export function ConfigMigrationWizard({ onDone }: { onDone: () => void }) {
       if (direction === 'local-to-saas' && localModels.length > 0) {
         // Push local models as config items
         for (const model of localModels) {
-          const exists = saasConfigs.some((c) => c.key_path === `models.${model.id}`);
-          if (exists && !selectedKeys.has(model.id)) continue;
+          const existing = saasConfigs.find((c) => c.key_path === `models.${model.id}`);
+          if (existing && !selectedKeys.has(model.id)) continue;
 
           const body = {
             category: 'model',
@@ -114,8 +114,8 @@ export function ConfigMigrationWizard({ onDone }: { onDone: () => void }) {
             description: `从桌面端同步: ${model.name}`,
           };
 
-          if (exists) {
-            await saasClient.request<unknown>('PUT', `/api/v1/config/items/${exists}`, body);
+          if (existing) {
+            await saasClient.request<unknown>('PUT', `/api/v1/config/items/${existing.id}`, body);
           } else {
             await saasClient.request<unknown>('POST', '/api/v1/config/items', body);
           }