Add mirroring action (#38)

Author: gspencergoog

.github/workflows/mirror.yml

@@ -0,0 +1,36 @@
+name: Mirror To gemini-cli-extensions/flutter
+
+on: [push, delete]
+
+# Ensures that only one mirror job runs at a time per branch.
+# Cancels any in-progress job on the same branch if a new push occurs.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  mirror:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Setup SSH and Push to Mirror
+        run: |
+          # 1. Start the ssh-agent
+          eval "$(ssh-agent -s)"
+
+          # 2. Add the SSH private key from the secret to the agent
+          echo "${{ secrets.SSH_PRIVATE_KEY }}" | ssh-add -
+
+          # 3. Add GitHub's public SSH keys to the known_hosts file for security.
+          # Keys are sourced from:
+          # https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/githubs-ssh-key-fingerprints
+          mkdir -p ~/.ssh
+          echo "
+          github.com ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOMqqnkVzrm0SdG6UOoqKLsabgH5C9okWi0dh2l9GKJl" >> ~/.ssh/known_hosts
+
+          # 4. Push to the destination repository
+          git push --mirror git@github.com:gemini-cli-extensions/flutter.git