fix: use github.repository instead of gitea.repository for image tagging

The gitea.repository context was empty in the CI environment, causing invalid Docker image references like 'registry/:<sha>'. Switching to github.repository ensures the repo name is populated and tags are valid.

.gitea/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
       - name: Set image name (lowercase)
         id: meta
         run: |
-          echo "repo=${{ toLower(gitea.repository) }}" >> $GITHUB_OUTPUT
+          echo "repo=${{ toLower(github.repository) }}" >> $GITHUB_OUTPUT
 
       - name: Log in to Gitea Container Registry
         uses: docker/login-action@v3