fix(desktop):add auth cutover ipc

surfsense_desktop/src/modules/auth-cutover.ts

@@ -0,0 +1,30 @@
+import { app } from 'electron';
+import { mkdir, readFile, writeFile } from 'node:fs/promises';
+import path from 'node:path';
+import { secretStore } from './secret-store';
+
+const CUTOVER_FLAG_FILE = 'auth-cutover-v1.json';
+const REFRESH_TOKEN_KEY = 'surfsense_refresh_token';
+
+async function hasCompletedCutover(flagPath: string): Promise<boolean> {
+  try {
+    const raw = await readFile(flagPath, 'utf8');
+    return JSON.parse(raw)?.complete === true;
+  } catch {
+    return false;
+  }
+}
+
+export async function purgeLegacyAuthCutover(): Promise<void> {
+  const userDataPath = app.getPath('userData');
+  const flagPath = path.join(userDataPath, CUTOVER_FLAG_FILE);
+  if (await hasCompletedCutover(flagPath)) return;
+
+  await secretStore.clear(REFRESH_TOKEN_KEY);
+  await mkdir(userDataPath, { recursive: true });
+  await writeFile(
+    flagPath,
+    JSON.stringify({ complete: true, completedAt: new Date().toISOString() }),
+    { mode: 0o600 }
+  );
+}