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/function-bind/.eslintrc

@@ -0,0 +1,21 @@
+{
+	"root": true,
+
+	"extends": "@ljharb",
+
+	"rules": {
+		"func-name-matching": 0,
+		"indent": [2, 4],
+		"no-new-func": [1],
+	},
+
+	"overrides": [
+		{
+			"files": "test/**",
+			"rules": {
+				"max-lines-per-function": 0,
+				"strict": [0]
+			},
+		},
+	],
+}