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/compile/rules.ts

@@ -0,0 +1,50 @@
+import type {AddedKeywordDefinition} from "../types"
+
+const _jsonTypes = ["string", "number", "integer", "boolean", "null", "object", "array"] as const
+
+export type JSONType = (typeof _jsonTypes)[number]
+
+const jsonTypes: Set<string> = new Set(_jsonTypes)
+
+export function isJSONType(x: unknown): x is JSONType {
+  return typeof x == "string" && jsonTypes.has(x)
+}
+
+type ValidationTypes = {
+  [K in JSONType]: boolean | RuleGroup | undefined
+}
+
+export interface ValidationRules {
+  rules: RuleGroup[]
+  post: RuleGroup
+  all: {[Key in string]?: boolean | Rule} // rules that have to be validated
+  keywords: {[Key in string]?: boolean} // all known keywords (superset of "all")
+  types: ValidationTypes
+}
+
+export interface RuleGroup {
+  type?: JSONType
+  rules: Rule[]
+}
+
+// This interface wraps KeywordDefinition because definition can have multiple keywords
+export interface Rule {
+  keyword: string
+  definition: AddedKeywordDefinition
+}
+
+export function getRules(): ValidationRules {
+  const groups: Record<"number" | "string" | "array" | "object", RuleGroup> = {
+    number: {type: "number", rules: []},
+    string: {type: "string", rules: []},
+    array: {type: "array", rules: []},
+    object: {type: "object", rules: []},
+  }
+  return {
+    types: {...groups, integer: true, boolean: true, null: true},
+    rules: [{rules: []}, groups.number, groups.string, groups.array, groups.object],
+    post: {rules: []},
+    all: {},
+    keywords: {},
+  }
+}