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/stringify-object/package.json

@@ -0,0 +1,40 @@
+{
+	"name": "stringify-object",
+	"version": "3.3.0",
+	"description": "Stringify an object/array like JSON.stringify just without all the double-quotes",
+	"license": "BSD-2-Clause",
+	"repository": "yeoman/stringify-object",
+	"author": {
+		"name": "Sindre Sorhus",
+		"email": "sindresorhus@gmail.com",
+		"url": "sindresorhus.com"
+	},
+	"engines": {
+		"node": ">=4"
+	},
+	"scripts": {
+		"test": "xo && ava"
+	},
+	"files": [
+		"index.js"
+	],
+	"keywords": [
+		"object",
+		"stringify",
+		"pretty",
+		"print",
+		"dump",
+		"format",
+		"type",
+		"json"
+	],
+	"dependencies": {
+		"get-own-enumerable-property-symbols": "^3.0.0",
+		"is-obj": "^1.0.1",
+		"is-regexp": "^1.0.0"
+	},
+	"devDependencies": {
+		"ava": "*",
+		"xo": "*"
+	}
+}