fix: minimize Nextcloud workflow patches

[vitormattos]

Summary

Reduce downstream divergence from Nextcloud workflow templates and restore materialized organization templates.

Policy applied in this PR:

• preserve Nextcloud workflow contents verbatim whenever they already work for LibreCode;
• patch only infrastructure incompatibilities;
• do not rename steps, rewrite shell snippets, reformat YAML, replace secrets.GITHUB_TOKEN, or otherwise refactor upstream code;
• preserve upstream SPDX copyright/license headers;
• keep consumer-specific differences out of the organization-level patch.

The materialized templates now differ from Nextcloud only where required:

• organization catalog URL points to LibreCodeCoop/.github;
• ubuntu-latest-low is replaced with GitHub-hosted ubuntu-latest;
• appstore-build-publish.yml removes the Nextcloud-only nextcloud-releases owner guard;
• the already-reviewed workflow synchronization patch remains responsible for LibreCode catalog and GitHub App integration.

The old reusable workflows in .github/workflows/ are intentionally left in place for compatibility with consumers pinned to historical SHAs, but the upstream render pipeline no longer generates them. New catalog output is materialized under workflow-templates/.