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/workbox-recipes/tsconfig.json

@@ -0,0 +1,17 @@
+{
+  "extends": "../../tsconfig",
+  "compilerOptions": {
+    "outDir": "./",
+    "rootDir": "./src",
+    "tsBuildInfoFile": "./tsconfig.tsbuildinfo"
+  },
+  "include": ["src/**/*.ts"],
+  "references": [
+    {"path": "../workbox-core/"},
+    {"path": "../workbox-routing/"},
+    {"path": "../workbox-strategies/"},
+    {"path": "../workbox-cacheable-response/"},
+    {"path": "../workbox-expiration/"},
+    {"path": "../workbox-precaching/"}
+  ]
+}