fix: keep release checks green for the note CSS preview and undo test

ParentNode.append is the Workers stream helper under the root typecheck, so the preview attaches DOM nodes with appendChild. The sync queue test restores navigator after forcing onLine, so a later headless TipTap test can still read userAgent.

tests/web-sync-queue.test.ts

@@ -15,6 +15,7 @@ const {
 } = await import("../apps/web/src/lib/sync-queue");
 const { formatLocalDraftClipboardText } = await import("../apps/web/src/lib/memo-save-conflict");
 const originalFetch = globalThis.fetch;
+const originalNavigator = Object.getOwnPropertyDescriptor(globalThis, "navigator");
 
 const payload = (title: string, revision = 0): MemoUpdateSyncPayload => ({
   memoId: "memo_sync_test",
@@ -76,6 +77,11 @@ beforeEach(async () => {
 
 afterEach(() => {
   globalThis.fetch = originalFetch;
+  if (originalNavigator) {
+    Object.defineProperty(globalThis, "navigator", originalNavigator);
+  } else {
+    delete globalThis.navigator;
+  }
 });
 
 describe("web sync queue concurrency", () => {