[Backend] feat(git): software-core::git -- Git feature to handle ADJ updates

[pminmic]

• Add ADJ repository management behind the git feature using gix.
• Shallow-clone the requested branch and replace the local cache after a successful checkout.
• Preserve the existing cache if cloning fails, with rollback protection during replacement.
• Support offline startup using cached ADJ, returning an error when no local repository is available.
• Return the checked-out commit hash and message.
• Add helpers for opening repositories and inspecting cached remote branches.
• Include tracing logs, Rustdoc documentation, and an README.
• Add local-repository tests for branch selection, cache replacement, and failure handling.