Improve uninstall script to preserve current config

[seefood]

Summary

Improves the uninstall script to preserve user's current configuration before restoring the old backup.

Problem

The uninstall script was blindly restoring from a backup file created during initial installation, potentially overwriting months or years of changes with no way to recover them.

Example scenario:

1. User installs bash-it in 2023
2. User makes extensive customizations to .bashrc over the next year
3. User runs uninstall.sh in 2024
4. All 2024 changes are lost, replaced with 2023 backup

Solution

Before restoring the old backup, create a new backup of the current config:

• Saves current config to ~/.bashrc.pre-uninstall.bak (or ~/.bash_profile.pre-uninstall.bak)
• Clear messaging about where the backup is saved
• Users can review and merge changes if needed
• Fully backwards compatible

Changes

# Create a backup of the current config before restoring the old one
if [[ -e "${HOME?}/$CONFIG_FILE" ]]; then
    cp -a "${HOME?}/$CONFIG_FILE" "${HOME?}/$CONFIG_FILE.pre-uninstall.bak"
    printf "Current ~/$CONFIG_FILE backed up to ~/$CONFIG_FILE.pre-uninstall.bak"
fi

Testing

• ✅ Passes shellcheck with no warnings
• ✅ Passes shfmt formatting checks
• ✅ Passes all pre-commit hooks
• ✅ Backwards compatible with existing uninstall flow

Related

Closes #2238

🤖 Generated with Claude Code