### CHANGES
- Add `getSortedGroupsItems` to centralize sorting logic.
- Sort groups and items alphabetically, case-insensitive.
- Replace inline sorting in `Print` with new method.
- Update `GetGroupAndItemByItemNumber` to use sorted data.
- Ensure original `GroupsItems` remains unmodified.
CHANGES:
- Add shell completion support for three major shells
- Create standardized completion scripts in completions/ directory
- Add --shell-complete-list flag for machine-readable output
- Update Print() methods to support plain output format
- Document installation steps for each shell in README
- Replace old fish completion script with improved version
### CHANGES
- Import `sort` and `strings` packages for sorting functionality.
- Create a copy of groups for stable sorting.
- Sort groups alphabetically in a case-insensitive manner.
- Create a copy of items within each group for sorting.
- Sort items alphabetically in a case-insensitive manner.
- Iterate over sorted groups and items for display.
