feat(gitutil): release v1.9.0 — detached HEAD support in CI

- CurrentBranch falls back to CI_COMMIT_BRANCH, CI_COMMIT_REF_NAME, then
  GITHUB_REF_NAME when HEAD is detached, so --branch is no longer required
  in GitLab CI / GitHub Actions jobs
- go-git push paths (token and SSH agent) now push HEAD's commit hash to
  the branch instead of refs/heads/<branch>, which never exists in a
  detached CI checkout — go-git silently skipped the branch update and
  pushed only the tag
- .releaser.gitlab-ci.yml template drops the redundant --branch flag
- docs: README, usage, ci-integration, changelog, ROADMAP updated

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/content/changelog.md

@@ -3,6 +3,16 @@ title: Changelog
 weight: 50
 ---
 
+## v1.9.0 — 2026-07-16
+
+### Added
+
+- **CI branch detection fallback** — on detached HEAD, the branch name falls back to `CI_COMMIT_BRANCH`, then `CI_COMMIT_REF_NAME` (GitLab CI), then `GITHUB_REF_NAME` (GitHub Actions); `--branch` is no longer required in CI
+
+### Fixed
+
+- **Detached HEAD push** — go-git pushes silently skipped the branch update in detached CI checkouts (only the tag was pushed); the branch is now pushed from HEAD's commit hash
+
 ## v1.8.0 — 2026-07-12
 
 ### Added