Add sync error logging, extend error flash, fix unload saves

- Log workforce sync errors to backend stdout so they appear in docker logs
- Extend error flash from 5s to 15s so errors are readable
- Replace sendBeacon (POST-only) with keepalive fetch (PUT) on unload —
  sendBeacon was hitting 404s on all three unload saves

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/node_modules/@trickfilm400/rollup-plugin-off-main-thread/tests/import-meta.test.js

@@ -0,0 +1,33 @@
+/**
+ * Copyright 2018 Google Inc. All Rights Reserved.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+describe("import.meta", function() {
+  beforeEach(function() {
+    this.ifr = document.createElement("iframe");
+    document.body.append(this.ifr);
+  });
+
+  afterEach(function() {
+    this.ifr.remove();
+  });
+
+  it("loads transpiled modules", function(done) {
+    window.addEventListener("message", function l(ev) {
+      if (/^https?:\/\/.+\.js$/.test(ev.data)) {
+        window.removeEventListener("message", l);
+        done();
+      }
+    });
+    this.ifr.src = "/base/tests/fixtures/import-meta/build/runner.html";
+  });
+});