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/applicator/dependencies.d.ts

@@ -0,0 +1,21 @@
+import type { CodeKeywordDefinition, ErrorObject, KeywordErrorDefinition, SchemaMap, AnySchema } from "../../types";
+import type { KeywordCxt } from "../../compile/validate";
+export type PropertyDependencies = {
+    [K in string]?: string[];
+};
+export interface DependenciesErrorParams {
+    property: string;
+    missingProperty: string;
+    depsCount: number;
+    deps: string;
+}
+export type DependenciesError = ErrorObject<"dependencies", DependenciesErrorParams, {
+    [K in string]?: string[] | AnySchema;
+}>;
+export declare const error: KeywordErrorDefinition;
+declare const def: CodeKeywordDefinition;
+export declare function validatePropertyDeps(cxt: KeywordCxt, propertyDeps?: {
+    [K in string]?: string[];
+}): void;
+export declare function validateSchemaDeps(cxt: KeywordCxt, schemaDeps?: SchemaMap): void;
+export default def;