The database stores short branch names (e.g., "main"), but git2's push_ref()
requires full reference names (e.g., "refs/heads/main"). This fixes all
service-layer endpoints to convert default_branch to the full ref format.
Fixed endpoints:
- git_readme: convert to refs/heads/{branch}
- git_commit_count: convert to refs/heads/{branch}
- git_contributors: convert to refs/heads/{branch}
- git_commit_log: convert to refs/heads/{branch}
- git_commit_walk: convert to refs/heads/{branch}
Resolves errors:
- Internal("the given reference name 'main' is not valid")
82ed726848