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/parser/bin/babel-parser.js

@@ -0,0 +1,15 @@
+#!/usr/bin/env node
+/* eslint-disable no-var, unicorn/prefer-node-protocol */
+
+var parser = require("..");
+var fs = require("fs");
+
+var filename = process.argv[2];
+if (!filename) {
+  console.error("no filename specified");
+} else {
+  var file = fs.readFileSync(filename, "utf8");
+  var ast = parser.parse(file);
+
+  console.log(JSON.stringify(ast, null, "  "));
+}