refactor: remove GitLab CI config and docs after full Gitea migration

- Delete .gitlab-ci.yml (replaced by .gitea/workflows/ci.yml)
- Delete docs/deployment/gitlab.md (superseded by gitea.md)
- Update audit rules to reference .gitea/workflows/*.yml
- Update validate_audit.py to check Gitea CI paths
- Clean up GitLab references in gitea.md, mkdocs.yml, .dockerignore
- Mark IPv6 AAAA records as completed in hetzner docs

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

.gitea/workflows/ci.yml

@@ -1,6 +1,6 @@
 # Gitea Actions CI/CD Configuration
 # ==================================
-# Equivalent of the GitLab CI pipeline, using GitHub Actions-compatible syntax.
+# Uses GitHub Actions-compatible syntax. Requires Gitea 1.19+ with Actions enabled.
 # Requires Gitea 1.19+ with Actions enabled.
 
 name: CI