Fix crash when opening a repo with no commits and a remote

[evanrichter]

I found an edge case that crashes gitu on startup when run in a fresh clone of a new/empty repo.

When a git repository has no commits but has a remote configured, git status --porcelain --branch outputs:

## No commits yet on main...origin/main [gone]

The status parser only handled the simple case (## No commits yet on main) and failed to parse the remote and [gone] suffix, causing a panic at src/git/mod.rs:174.

This PR updates parse_no_commits to handle the optional remote branch and ahead/behind info (like [gone]), following the same logic as parse_branch_status.

Steps to reproduce:

git clone <new-empty-repo>
cd <repo>
gitu  # panics

Error:

panicked at src/git/mod.rs:174:40:
called `Result::unwrap()` on an `Err` value: "Failed to parse status: Error(Error { input: "...origin/main [gone]\n", code: CrLf })"

Checklist

• The modified code has some test-coverage (where applicable).
• make test is passing (this is what CI runs).
• New unreleased features/fixes/styling and performance improvements are documented via git: feat: / fix: / style: / perf:. Or e.g. perf(highlighting):.
  See https://github.com/altsem/gitu/blob/master/docs/dev-tooling.md