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/@isaacs/cliui/dist/commonjs/strip-ansi/index.js

@@ -0,0 +1,8 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.stripAnsi = void 0;
+const index_js_1 = require("../ansi-regex/index.js");
+const regex = (0, index_js_1.ansiRegex)();
+const stripAnsi = (str) => str.replace(regex, "");
+exports.stripAnsi = stripAnsi;
+//# sourceMappingURL=index.js.map