refactor(hooks): introduce unified post-change sync utility

- Add postChangeSync.ts utility with Result pattern for graceful error handling
- Replace try-catch with syncCurrentProvidersLiveSafe in useImportExport
- Add directory-change-triggered sync in useSettings to maintain SSOT
- Introduce partial-success status to distinguish import success from sync failures
- Add test coverage for sync behavior in different scenarios

This refactoring ensures config.json changes are reliably synced to live
files while providing better user feedback for edge cases.

src/utils/postChangeSync.ts

@@ -0,0 +1,19 @@
+import { settingsApi } from "@/lib/api";
+
+/**
+ * 统一的“后置同步”工具：将当前使用的供应商写回对应应用的 live 配置。
+ * 不抛出异常，由调用方根据返回值决定提示策略。
+ */
+export async function syncCurrentProvidersLiveSafe(): Promise<{
+  ok: boolean;
+  error?: Error;
+}> {
+  try {
+    await settingsApi.syncCurrentProvidersLive();
+    return { ok: true };
+  } catch (err) {
+    const error = err instanceof Error ? err : new Error(String(err ?? ""));
+    return { ok: false, error };
+  }
+}
+