feat: test GitFlow in an isolated project

Plan

1. Add version/namespace inputs and the common and GitFlow components.
2. Verify real default-branch settings and both protected branches.
3. Exercise the configured release branch and connect catalog integration tests.

Acceptance criteria

• Inputs default to main and xrow-public/ci-tools.
• Real configuration checks verify main and the configured development branch.
• Required MR job runs the tested revision's existing GitFlow regressions.
• Catalog CI_JOB_TOKEN access is allowlisted; project description is configured.
• GitLab CI lint and default-branch simulation pass.
• Required MR and complete default-branch integration CI succeed.

Closes #1 (closed).

Related to xrow-public/ci-tools#417 (closed).

Development branch decision

Use permanent chore/develop as the explicitly configured development branch, with normal GitFlow protection (Developer push, Maintainer merge). This exercises the supported custom branch input and real release guard while satisfying the required MR helper source-prefix policy. No hotfix bypass is enabled; squash must stay disabled for this release MR. Default develop behavior remains covered by the catalog's existing mocked regressions.

Closes #1 (closed)

Complete MR proof: https://gitlab.com/xrow-public/test-projects/workflow-gitflow/-/pipelines/2981667127. Complete default-branch proof: https://gitlab.com/xrow-public/test-projects/workflow-gitflow/-/pipelines/2981676514. Configuration, main/custom development branch protection assertions and release job all pass. Original CI config path is restored.