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/compile/names.d.ts

@@ -0,0 +1,20 @@
+import { Name } from "./codegen";
+declare const names: {
+    data: Name;
+    valCxt: Name;
+    instancePath: Name;
+    parentData: Name;
+    parentDataProperty: Name;
+    rootData: Name;
+    dynamicAnchors: Name;
+    vErrors: Name;
+    errors: Name;
+    this: Name;
+    self: Name;
+    scope: Name;
+    json: Name;
+    jsonPos: Name;
+    jsonLen: Name;
+    jsonPart: Name;
+};
+export default names;