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/test/.eslintrc

@@ -0,0 +1,9 @@
+{
+	"rules": {
+		"array-bracket-newline": 0,
+		"array-element-newline": 0,
+		"max-statements-per-line": [2, { "max": 2 }],
+		"no-invalid-this": 0,
+		"no-magic-numbers": 0,
+	}
+}