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/cross-spawn/lib/enoent.js

@@ -0,0 +1,59 @@
+'use strict';
+
+const isWin = process.platform === 'win32';
+
+function notFoundError(original, syscall) {
+    return Object.assign(new Error(`${syscall} ${original.command} ENOENT`), {
+        code: 'ENOENT',
+        errno: 'ENOENT',
+        syscall: `${syscall} ${original.command}`,
+        path: original.command,
+        spawnargs: original.args,
+    });
+}
+
+function hookChildProcess(cp, parsed) {
+    if (!isWin) {
+        return;
+    }
+
+    const originalEmit = cp.emit;
+
+    cp.emit = function (name, arg1) {
+        // If emitting "exit" event and exit code is 1, we need to check if
+        // the command exists and emit an "error" instead
+        // See https://github.com/IndigoUnited/node-cross-spawn/issues/16
+        if (name === 'exit') {
+            const err = verifyENOENT(arg1, parsed);
+
+            if (err) {
+                return originalEmit.call(cp, 'error', err);
+            }
+        }
+
+        return originalEmit.apply(cp, arguments); // eslint-disable-line prefer-rest-params
+    };
+}
+
+function verifyENOENT(status, parsed) {
+    if (isWin && status === 1 && !parsed.file) {
+        return notFoundError(parsed.original, 'spawn');
+    }
+
+    return null;
+}
+
+function verifyENOENTSync(status, parsed) {
+    if (isWin && status === 1 && !parsed.file) {
+        return notFoundError(parsed.original, 'spawnSync');
+    }
+
+    return null;
+}
+
+module.exports = {
+    hookChildProcess,
+    verifyENOENT,
+    verifyENOENTSync,
+    notFoundError,
+};