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/next.js

@@ -0,0 +1,8 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+const dependentRequired_1 = require("./validation/dependentRequired");
+const dependentSchemas_1 = require("./applicator/dependentSchemas");
+const limitContains_1 = require("./validation/limitContains");
+const next = [dependentRequired_1.default, dependentSchemas_1.default, limitContains_1.default];
+exports.default = next;
+//# sourceMappingURL=next.js.map