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/nullable.js

@@ -0,0 +1,22 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.checkNullableObject = exports.checkNullable = void 0;
+const codegen_1 = require("../../compile/codegen");
+function checkNullable({ gen, data, parentSchema }, cond = codegen_1.nil) {
+    const valid = gen.name("valid");
+    if (parentSchema.nullable) {
+        gen.let(valid, (0, codegen_1._) `${data} === null`);
+        cond = (0, codegen_1.not)(valid);
+    }
+    else {
+        gen.let(valid, false);
+    }
+    return [valid, cond];
+}
+exports.checkNullable = checkNullable;
+function checkNullableObject(cxt, cond) {
+    const [valid, cond_] = checkNullable(cxt, cond);
+    return [valid, (0, codegen_1._) `${cond_} && typeof ${cxt.data} == "object" && !Array.isArray(${cxt.data})`];
+}
+exports.checkNullableObject = checkNullableObject;
+//# sourceMappingURL=nullable.js.map