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/es-abstract/2025/tables/typed-array-objects.js

@@ -0,0 +1,38 @@
+'use strict';
+
+// https://262.ecma-international.org/16.0/#table-the-typedarray-constructors
+
+module.exports = {
+	__proto__: null,
+	name: {
+		__proto__: null,
+		$Int8Array: 'INT8',
+		$Uint8Array: 'UINT8',
+		$Uint8ClampedArray: 'UINT8C',
+		$Int16Array: 'INT16',
+		$Uint16Array: 'UINT16',
+		$Int32Array: 'INT32',
+		$Uint32Array: 'UINT32',
+		$BigInt64Array: 'BIGINT64',
+		$BigUint64Array: 'BIGUINT64',
+		$Float16Array: 'FLOAT16',
+		$Float32Array: 'FLOAT32',
+		$Float64Array: 'FLOAT64'
+	},
+	size: {
+		__proto__: null,
+		$INT8: 1,
+		$UINT8: 1,
+		$UINT8C: 1,
+		$INT16: 2,
+		$UINT16: 2,
+		$INT32: 4,
+		$UINT32: 4,
+		$BIGINT64: 8,
+		$BIGUINT64: 8,
+		$FLOAT16: 2,
+		$FLOAT32: 4,
+		$FLOAT64: 8
+	},
+	choices: '"INT8", "UINT8", "UINT8C", "INT16", "UINT16", "INT32", "UINT32", "BIGINT64", "BIGUINT64", "FLOAT16", "FLOAT32", or "FLOAT64"'
+};