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-validator-option/lib/validator.js

@@ -0,0 +1,48 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.OptionValidator = void 0;
+var _findSuggestion = require("./find-suggestion.js");
+class OptionValidator {
+  constructor(descriptor) {
+    this.descriptor = descriptor;
+  }
+  validateTopLevelOptions(options, TopLevelOptionShape) {
+    const validOptionNames = Object.keys(TopLevelOptionShape);
+    for (const option of Object.keys(options)) {
+      if (!validOptionNames.includes(option)) {
+        throw new Error(this.formatMessage(`'${option}' is not a valid top-level option.
+- Did you mean '${(0, _findSuggestion.findSuggestion)(option, validOptionNames)}'?`));
+      }
+    }
+  }
+  validateBooleanOption(name, value, defaultValue) {
+    if (value === undefined) {
+      return defaultValue;
+    } else {
+      this.invariant(typeof value === "boolean", `'${name}' option must be a boolean.`);
+    }
+    return value;
+  }
+  validateStringOption(name, value, defaultValue) {
+    if (value === undefined) {
+      return defaultValue;
+    } else {
+      this.invariant(typeof value === "string", `'${name}' option must be a string.`);
+    }
+    return value;
+  }
+  invariant(condition, message) {
+    if (!condition) {
+      throw new Error(this.formatMessage(message));
+    }
+  }
+  formatMessage(message) {
+    return `${this.descriptor}: ${message}`;
+  }
+}
+exports.OptionValidator = OptionValidator;
+
+//# sourceMappingURL=validator.js.map