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/object-inspect/test/deep.js

@@ -0,0 +1,12 @@
+var inspect = require('../');
+var test = require('tape');
+
+test('deep', function (t) {
+    t.plan(4);
+    var obj = [[[[[[500]]]]]];
+    t.equal(inspect(obj), '[ [ [ [ [ [Array] ] ] ] ] ]');
+    t.equal(inspect(obj, { depth: 4 }), '[ [ [ [ [Array] ] ] ] ]');
+    t.equal(inspect(obj, { depth: 2 }), '[ [ [Array] ] ]');
+
+    t.equal(inspect([[[{ a: 1 }]]], { depth: 3 }), '[ [ [ [Object] ] ] ]');
+});