Add the missing reporter change note for R2B JSON controls

The newly rerun CI for #5989 exposed the existing reporter-package change without its release note. Describe the already-implemented pass-through separator behavior; no runtime code or gate changes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 4747f826-8c83-495d-80df-3d1168662e10

Author: TheLarkInn

common/changes/@rushstack/rush-reporter/reporter-r2b-json-controls_2026-09-07.json

@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "@rushstack/rush-reporter",
+      "comment": "Honor the pass-through separator when distinguishing command JSON from reporter JSON controls.",
+      "type": "patch"
+    }
+  ],
+  "packageName": "@rushstack/rush-reporter",
+  "email": "223556219+Copilot@users.noreply.github.com"
+}