chore: add post-push mirror rule

Ensure pushes are mirrored when remote exists.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: pRizz

.cursor/rules/post-push-mirror.mdc

@@ -0,0 +1,10 @@
+---
+description: Post-push: also push to mirror remote when configured
+alwaysApply: true
+---
+
+# Post-Push Mirror Remote
+
+- After any successful `git push`, also run `git push mirror`.
+- Only do this if a remote named `mirror` exists (check `git remote -v`).
+- If `mirror` is not configured, ignore this rule.