chore: add change file for fast-router

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: janechu

change/@microsoft-fast-router-de58ce36-92f3-4c7f-86a2-43a66a522f81.json

@@ -0,0 +1,7 @@
+{
+  "type": "prerelease",
+  "comment": "Update imports for styles.js subpath export",
+  "packageName": "@microsoft/fast-router",
+  "email": "7559015+janechu@users.noreply.github.com",
+  "dependentChangeType": "none"
+}