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/shebang-regex/package.json

@@ -0,0 +1,35 @@
+{
+	"name": "shebang-regex",
+	"version": "3.0.0",
+	"description": "Regular expression for matching a shebang line",
+	"license": "MIT",
+	"repository": "sindresorhus/shebang-regex",
+	"author": {
+		"name": "Sindre Sorhus",
+		"email": "sindresorhus@gmail.com",
+		"url": "sindresorhus.com"
+	},
+	"engines": {
+		"node": ">=8"
+	},
+	"scripts": {
+		"test": "xo && ava && tsd"
+	},
+	"files": [
+		"index.js",
+		"index.d.ts"
+	],
+	"keywords": [
+		"regex",
+		"regexp",
+		"shebang",
+		"match",
+		"test",
+		"line"
+	],
+	"devDependencies": {
+		"ava": "^1.4.1",
+		"tsd": "^0.7.2",
+		"xo": "^0.24.0"
+	}
+}