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/applicator/dependentSchemas.js

@@ -0,0 +1,11 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+const dependencies_1 = require("./dependencies");
+const def = {
+    keyword: "dependentSchemas",
+    type: "object",
+    schemaType: "object",
+    code: (cxt) => (0, dependencies_1.validateSchemaDeps)(cxt),
+};
+exports.default = def;
+//# sourceMappingURL=dependentSchemas.js.map