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/@babel/preset-env/lib/polyfills/babel-7-plugins.cjs

@@ -0,0 +1,19 @@
+Object.defineProperties(exports, {
+  pluginCoreJS2: {
+    get: () => require("babel-plugin-polyfill-corejs2").default
+  },
+  pluginRegenerator: {
+    get: () => require("babel-plugin-polyfill-regenerator").default
+  },
+  legacyBabelPolyfillPlugin: {
+    get: () => require("./babel-polyfill.cjs")
+  },
+  removeRegeneratorEntryPlugin: {
+    get: () => require("./regenerator.cjs")
+  },
+  corejs2Polyfills: {
+    get: () => require("@babel/compat-data/corejs2-built-ins")
+  }
+});
+
+//# sourceMappingURL=babel-7-plugins.cjs.map