test: end-to-end brownfield (import) path validation before v0.1.0

[kameshsampath]

Context

The import path (step-1c-import-repo.md for GitHub, step-1c-import-project.md for GitLab) adds CoCo CI files to an existing repo and merges .gitlab-ci.yml if one exists. This path has not been tested end-to-end against a real existing repo with an active CI pipeline.

Test scenarios needed

1. Clean existing repo (no CI) — import should add all files without conflicts
2. Repo with existing .github/workflows/ — files should be added alongside existing workflows
3. GitLab project with existing .gitlab-ci.yml — CoCo jobs should be appended cleanly; check for merge conflicts
4. Repo with existing branch protection — quick start should detect and preserve existing rules (not overwrite)

Acceptance criteria

• All 4 scenarios complete without manual intervention
• Manifest correctly records IMPORT_MODE = true and project path
• Quick start path re-enables CI and leaves repo in a runnable state
• Full setup path runs smoke test successfully

Notes

Test before tagging v0.1.0. This is the most likely failure path for real users (most interesting repos already have CI).