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/get-intrinsic/.eslintrc

@@ -0,0 +1,42 @@
+{
+	"root": true,
+
+	"extends": "@ljharb",
+
+	"env": {
+		"es6": true,
+		"es2017": true,
+		"es2020": true,
+		"es2021": true,
+		"es2022": true,
+	},
+
+	"globals": {
+		"Float16Array": false,
+	},
+
+	"rules": {
+		"array-bracket-newline": 0,
+		"complexity": 0,
+		"eqeqeq": [2, "allow-null"],
+		"func-name-matching": 0,
+		"id-length": 0,
+		"max-lines": 0,
+		"max-lines-per-function": [2, 90],
+		"max-params": [2, 4],
+		"max-statements": 0,
+		"max-statements-per-line": [2, { "max": 2 }],
+		"multiline-comment-style": 0,
+		"no-magic-numbers": 0,
+		"sort-keys": 0,
+	},
+
+	"overrides": [
+		{
+			"files": "test/**",
+			"rules": {
+				"new-cap": 0,
+			},
+		},
+	],
+}