Handle detached HEAD and invalid remote URL; add tests to improve coverage

[zhaochunqi]

Motivation

• Avoid producing incorrect branch URLs when the repository is in a detached HEAD state by treating non-branch HEAD as an error instead of returning HEAD as a branch name.
• Prevent attempting to open an empty/invalid web URL by validating the result of convertToWebURL early.
• Improve unit test coverage for these edge cases so behavior is well-specified and regressions are caught.

Description

• Hardened branch resolution in getBranchName (in cmd/git.go) to return a clear error when repo.Head() points to a non-branch (detached HEAD) and fall back to reference lookup only if necessary.
• Added validation in rootCmd.RunE (in cmd/root.go) to return an error when convertToWebURL(remoteURL) yields an empty string.
• Added cmd/git_additional_test.go with Test_getBranchName_DetachedHEAD to cover the detached-HEAD path for getBranchName.
• Added cmd/root_additional_test.go with Test_rootCmd_InvalidRemoteURLFormat to assert rootCmd.RunE errors on unsupported remote URL formats.

Testing

• Attempted to run go test ./... -coverprofile=coverage.out, but the Go toolchain is not available in this environment (go: command not found).
• Attempted to run gofmt -w on modified files, but gofmt is not available in this environment (gofmt: command not found).
• New unit tests were added (cmd/git_additional_test.go, cmd/root_additional_test.go) and exercise the new code paths, but they were not executed here due to the missing Go toolchain.
• No automated test failures were observed within the repository actions performed locally (formatting and test execution were not possible in this environment).

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Codex Task

[zhaochunqi]

@codex

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.46%. Comparing base (3013c9d) to head (aed4d72).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #42      +/-   ##
==========================================
+ Coverage   96.10%   97.46%   +1.36%     
==========================================
  Files           5        5              
  Lines         154      158       +4     
==========================================
+ Hits          148      154       +6     
+ Misses          5        2       -3     
- Partials        1        2       +1     

Flag	Coverage Δ
unittests	97.46% <100.00%> (+1.36%)	⬆️

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[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Nice work!

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