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/ajv/dist/vocabularies/jtd/error.js

@@ -0,0 +1,20 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.typeErrorParams = exports.typeErrorMessage = exports.typeError = void 0;
+const codegen_1 = require("../../compile/codegen");
+function typeError(t) {
+    return {
+        message: (cxt) => typeErrorMessage(cxt, t),
+        params: (cxt) => typeErrorParams(cxt, t),
+    };
+}
+exports.typeError = typeError;
+function typeErrorMessage({ parentSchema }, t) {
+    return (parentSchema === null || parentSchema === void 0 ? void 0 : parentSchema.nullable) ? `must be ${t} or null` : `must be ${t}`;
+}
+exports.typeErrorMessage = typeErrorMessage;
+function typeErrorParams({ parentSchema }, t) {
+    return (0, codegen_1._) `{type: ${t}, nullable: ${!!(parentSchema === null || parentSchema === void 0 ? void 0 : parentSchema.nullable)}}`;
+}
+exports.typeErrorParams = typeErrorParams;
+//# sourceMappingURL=error.js.map