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/react-router-dom/dist/server.d.ts

@@ -0,0 +1,31 @@
+import * as React from "react";
+import type { Router as RemixRouter, StaticHandlerContext, CreateStaticHandlerOptions as RouterCreateStaticHandlerOptions, FutureConfig as RouterFutureConfig } from "@remix-run/router";
+import type { FutureConfig, Location, RouteObject } from "react-router-dom";
+export interface StaticRouterProps {
+    basename?: string;
+    children?: React.ReactNode;
+    location: Partial<Location> | string;
+    future?: Partial<FutureConfig>;
+}
+/**
+ * A `<Router>` that may not navigate to any other location. This is useful
+ * on the server where there is no stateful UI.
+ */
+export declare function StaticRouter({ basename, children, location: locationProp, future, }: StaticRouterProps): React.JSX.Element;
+export { StaticHandlerContext };
+export interface StaticRouterProviderProps {
+    context: StaticHandlerContext;
+    router: RemixRouter;
+    hydrate?: boolean;
+    nonce?: string;
+}
+/**
+ * A Data Router that may not navigate to any other location. This is useful
+ * on the server where there is no stateful UI.
+ */
+export declare function StaticRouterProvider({ context, router, hydrate, nonce, }: StaticRouterProviderProps): React.JSX.Element;
+type CreateStaticHandlerOptions = Omit<RouterCreateStaticHandlerOptions, "detectErrorBoundary" | "mapRouteProperties">;
+export declare function createStaticHandler(routes: RouteObject[], opts?: CreateStaticHandlerOptions): import("@remix-run/router").StaticHandler;
+export declare function createStaticRouter(routes: RouteObject[], context: StaticHandlerContext, opts?: {
+    future?: Partial<Pick<RouterFutureConfig, "v7_partialHydration" | "v7_relativeSplatPath">>;
+}): RemixRouter;