When a child bottle declares a git-gate repo with the same name as a
parent repo, merge field-by-field (child wins, parent provides fallback)
instead of letting the child entry silently replace the parent entry.
This lets a child override only `key:` without repeating `url:` and
`host_key:`. Change the merge key in _merge_git_remotes from UpstreamHost
to Name, which is the natural unique identity for a repo entry.
Closes#237
didericis-claude
4ed6b84863