Add sort-only mode feature (Issue #9)

[dvrkni]

Summary

• Implements issue [Feature] Sort only option #9: Sort only option that allows sorting YAML files without performing any diffing operations
• Adds new --sort-only CLI flag for sort-only mode
• Provides configuration file support with sort_only option
• Updates README.md with comprehensive documentation and examples

Features Added

• New CLI flag: --sort-only enables sort-only mode
• Configuration support: sort_only: true in config files
• Pattern matching: Works with both individual files and glob patterns
• Output flexibility: Supports in-place modification (-i) and custom output directories (-o)
• Validation: Requires and validates sort configuration file
• Workflow isolation: Complete separation from diff functionality

Usage Examples

# Sort files and output to ./out directory
./yabe --sort-only --sort-config-path sort-config.yaml file1.yaml file2.yaml

# Sort files in-place (modify original files)
./yabe --sort-only --sort-config-path sort-config.yaml -i file1.yaml file2.yaml

# Sort files using path patterns
./yabe --sort-only --sort-config-path sort-config.yaml -p "*.yaml"

Test plan

• Basic sort functionality with single files
• In-place modification mode (-i flag)
• Path pattern matching (-p flag)
• Error handling for missing sort config
• Help documentation verification
• All existing tests continue to pass
• Configuration file support

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