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/lib/standalone/instance.ts

@@ -0,0 +1,36 @@
+import Ajv, {AnySchema, AnyValidateFunction, ErrorObject} from "../core"
+import standaloneCode from "."
+import * as requireFromString from "require-from-string"
+
+export default class AjvPack {
+  errors?: ErrorObject[] | null // errors from the last validation
+  constructor(readonly ajv: Ajv) {}
+
+  validate(schemaKeyRef: AnySchema | string, data: unknown): boolean | Promise<unknown> {
+    return Ajv.prototype.validate.call(this, schemaKeyRef, data)
+  }
+
+  compile<T = unknown>(schema: AnySchema, meta?: boolean): AnyValidateFunction<T> {
+    return this.getStandalone(this.ajv.compile<T>(schema, meta))
+  }
+
+  getSchema<T = unknown>(keyRef: string): AnyValidateFunction<T> | undefined {
+    const v = this.ajv.getSchema<T>(keyRef)
+    if (!v) return undefined
+    return this.getStandalone(v)
+  }
+
+  private getStandalone<T = unknown>(v: AnyValidateFunction<T>): AnyValidateFunction<T> {
+    return requireFromString(standaloneCode(this.ajv, v)) as AnyValidateFunction<T>
+  }
+
+  addSchema(...args: Parameters<typeof Ajv.prototype.addSchema>): AjvPack {
+    this.ajv.addSchema.call(this.ajv, ...args)
+    return this
+  }
+
+  addKeyword(...args: Parameters<typeof Ajv.prototype.addKeyword>): AjvPack {
+    this.ajv.addKeyword.call(this.ajv, ...args)
+    return this
+  }
+}