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/rules.d.ts

@@ -0,0 +1,28 @@
+import type { AddedKeywordDefinition } from "../types";
+declare const _jsonTypes: readonly ["string", "number", "integer", "boolean", "null", "object", "array"];
+export type JSONType = (typeof _jsonTypes)[number];
+export declare function isJSONType(x: unknown): x is JSONType;
+type ValidationTypes = {
+    [K in JSONType]: boolean | RuleGroup | undefined;
+};
+export interface ValidationRules {
+    rules: RuleGroup[];
+    post: RuleGroup;
+    all: {
+        [Key in string]?: boolean | Rule;
+    };
+    keywords: {
+        [Key in string]?: boolean;
+    };
+    types: ValidationTypes;
+}
+export interface RuleGroup {
+    type?: JSONType;
+    rules: Rule[];
+}
+export interface Rule {
+    keyword: string;
+    definition: AddedKeywordDefinition;
+}
+export declare function getRules(): ValidationRules;
+export {};