ci: add mirror-to-codeberg workflow

Automatically pushes main and dev to the Codeberg mirror
(codeberg.org/TMoussa/ConformalLabpp) after every push to eulernest.
Requires CODEBERG_TOKEN secret in the eulernest repo settings.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/mirror-to-codeberg.yml

@@ -0,0 +1,21 @@
+name: Mirror to Codeberg
+
+on:
+  push:
+    branches:
+      - main
+      - dev
+
+jobs:
+  mirror:
+    runs-on: eulernest
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0   # vollständige History für mirror-push
+
+      - name: Push to Codeberg mirror
+        run: |
+          git remote add codeberg https://TMoussa:${{ secrets.CODEBERG_TOKEN }}@codeberg.org/TMoussa/ConformalLabpp.git
+          git push codeberg HEAD:${{ github.ref_name }} --force