chore: add rush change file

Author: ItsChrisHickman

common/changes/@microsoft/api-extractor/fix-namespace-export-keyword_2025-12-24-17-25.json

@@ -0,0 +1,5 @@
+{
+  "packageName": "@microsoft/api-extractor",
+  "comment": "Fix missing 'export' keyword for namespace re-exports that produced invalid TypeScript output",
+  "type": "patch"
+}