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/jsonpointer/jsonpointer.d.ts

@@ -0,0 +1,35 @@
+interface JSONPointer {
+    /**
+     * Looks up a JSON pointer in an object
+     */
+    get(object: Object): any;
+
+
+    /**
+     * Set a value for a JSON pointer on object
+     */
+    set(object: Object, value: any): void;
+}
+
+
+declare namespace JSONPointer {
+    /**
+     * Looks up a JSON pointer in an object
+     */
+    function get(object: Object, pointer: string): any;
+
+
+    /**
+     * Set a value for a JSON pointer on object
+     */
+    function set(object: Object, pointer: string, value: any): void;
+
+
+    /**
+     *  Builds a JSONPointer instance from a pointer value.
+     */
+    function compile(pointer: string): JSONPointer;
+}
+
+
+export = JSONPointer;