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/helper-define-polyfill-provider/lib/visitors/entry.js

@@ -0,0 +1,26 @@
+"use strict";
+
+exports.__esModule = true;
+exports.default = void 0;
+var _utils = require("../utils");
+var _default = callProvider => ({
+  ImportDeclaration(path) {
+    const source = (0, _utils.getImportSource)(path);
+    if (!source) return;
+    callProvider({
+      kind: "import",
+      source
+    }, path);
+  },
+  Program(path) {
+    path.get("body").forEach(bodyPath => {
+      const source = (0, _utils.getRequireSource)(bodyPath);
+      if (!source) return;
+      callProvider({
+        kind: "import",
+        source
+      }, bodyPath);
+    });
+  }
+});
+exports.default = _default;