feat(docker): add Docker Hub authentication for CI/CD workflows

- Introduced `docker_hub_token` and `docker_hub_username` secrets for Docker Hub login in CI/CD workflows.
- Updated `.gitea/workflows/ci.yaml`, `.gitea/workflows/cd.yaml`, and `.gitea/workflows/quality.yaml` to utilize these secrets for Docker Hub authentication.
- Enhanced README and releasing documentation to clarify the use of Docker Hub credentials for image mirroring and builds.

deploy/docker/mirror-base-images.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env sh
 # Copy-by-digest зеркало базовых образов в Gitea Container Registry (без rebuild).
-# Требует: docker login в REGISTRY host, docker buildx.
+# Требует: docker login в REGISTRY host, docker login Docker Hub (CI: secrets.docker_hub_token), docker buildx.
 # REGISTRY=git.shx.one/<owner>  (без суффикса /evobgp-buildcache)
 #
 # Источник library-образов — Docker Hub (docker.io), не public.ecr.aws (429 Too Many Requests).