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/minimatch/dist/esm/assert-valid-pattern.js

@@ -0,0 +1,10 @@
+const MAX_PATTERN_LENGTH = 1024 * 64;
+export const assertValidPattern = (pattern) => {
+    if (typeof pattern !== 'string') {
+        throw new TypeError('invalid pattern');
+    }
+    if (pattern.length > MAX_PATTERN_LENGTH) {
+        throw new TypeError('pattern is too long');
+    }
+};
+//# sourceMappingURL=assert-valid-pattern.js.map