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- Delete docs/deployment/gitlab.md (superseded by gitea.md)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>

.audit-rules/third_party.yaml

@@ -57,7 +57,7 @@ rules:
       type: file_exists
       paths:
         - ".github/workflows/*.yml"
-        - ".gitlab-ci.yml"
+        - ".gitea/workflows/*.yml"
       patterns:
         - "safety|pip-audit|snyk|dependabot"
       message: "Dependency vulnerability scanning required"
@@ -70,7 +70,7 @@ rules:
       type: file_exists
       paths:
         - ".github/dependabot.yml"
-        - ".gitlab-ci.yml"  # GitLab uses built-in dependency scanning
+        - ".gitea/workflows/*.yml"
       message: "Consider enabling Dependabot for security updates"
 
   - id: THIRD-VULN-003
@@ -81,7 +81,7 @@ rules:
       type: pattern_recommended
       paths:
         - ".github/workflows/*.yml"
-        - ".gitlab-ci.yml"
+        - ".gitea/workflows/*.yml"
       patterns:
         - "trivy|grype|snyk.*container"
       message: "Consider container image vulnerability scanning"