fix: reject a malformed reenqueue body instead of running the full scope

Option<Json<T>> collapses a malformed body to None, so a bad reenqueue body
silently ran the default full "All" scope (audit). Parse raw bytes: empty =
default All, malformed = 422. Tested both.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.128.16",
+  "version": "0.128.17",
   "private": true,
   "type": "module",
   "scripts": {