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/package-support.json

@@ -0,0 +1,20 @@
+{
+  "versions": [
+    {
+      "version": "*",
+      "target": {
+        "node": "all"
+      },
+      "response": {
+        "type": "time-permitting"
+      },
+      "backing": {
+        "npm-funding": true,
+        "donations": [
+          "https://github.com/ljharb",
+          "https://tidelift.com/funding/github/npm/object-inspect"
+        ]
+      }
+    }
+  ]
+}