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/validation/limitProperties.js

@@ -0,0 +1,24 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+const codegen_1 = require("../../compile/codegen");
+const error = {
+    message({ keyword, schemaCode }) {
+        const comp = keyword === "maxProperties" ? "more" : "fewer";
+        return (0, codegen_1.str) `must NOT have ${comp} than ${schemaCode} properties`;
+    },
+    params: ({ schemaCode }) => (0, codegen_1._) `{limit: ${schemaCode}}`,
+};
+const def = {
+    keyword: ["maxProperties", "minProperties"],
+    type: "object",
+    schemaType: "number",
+    $data: true,
+    error,
+    code(cxt) {
+        const { keyword, data, schemaCode } = cxt;
+        const op = keyword === "maxProperties" ? codegen_1.operators.GT : codegen_1.operators.LT;
+        cxt.fail$data((0, codegen_1._) `Object.keys(${data}).length ${op} ${schemaCode}`);
+    },
+};
+exports.default = def;
+//# sourceMappingURL=limitProperties.js.map