fix(scripts): Show git checkout error output on branch creation failure

[grafvonb]

Summary

Improves error reporting in create-new-feature.sh by displaying actual git error messages instead of silently discarding them.

Problem

When git checkout -b or git checkout failed, stderr was discarded with 2>/dev/null. This left users without diagnostic information to troubleshoot issues like:

• Uncommitted changes blocking checkout
• Merge conflicts
• Permission problems
• Detached HEAD states

Solution

• Capture stderr from git checkout commands using file descriptor redirection
• Display the captured error message when operations fail
• Preserve existing error handling logic and exit codes

Testing

Tested by attempting branch operations with:

• Dirty working tree (shows "Please commit your changes or stash them")
• Existing branch without --allow-existing-branch flag

[mnriem]

You will also have to deliver the Powershell variant

[Copilot]

Pull request overview

Improves diagnostics in scripts/bash/create-new-feature.sh so users can see the underlying git checkout error output when branch creation/switching fails, aiding troubleshooting during feature branch setup.

Changes:

• Captures git checkout stderr into a variable instead of discarding it.
• Prints the captured stderr when branch creation/switching fails, while keeping existing branching logic and exit behavior.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

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[Copilot]

$checkoutStderr = git checkout ... 2>&1 | Out-String captures both stdout and stderr (it merges streams), so the variable name is a bit misleading and future changes to the git flags could accidentally include non-error output in the “stderr” blob. Consider either redirecting stdout away (while preserving stderr capture) or renaming the variable to reflect that it’s combined output.

[mnriem]

Please address Copilot feedback. Probably should reflect it is both