Fix Gitea registry login credentials

Use github.repository_owner and GITHUB_TOKEN for compatibility

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -29,8 +29,8 @@ jobs:
         uses: docker/login-action@v3
         with:
           registry: ${{ env.REGISTRY }}
-          username: ${{ gitea.actor }}
-          password: ${{ secrets.GITEA_TOKEN }}
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Extract metadata
         id: meta