refactor: restructure codebase with modular command and utility organization

[inureyes]

Summary

• Restructured codebase for better maintainability and scalability
• Reduced main.rs from 987 lines to ~150 lines (84% reduction)
• Separated commands into individual modules for better testability

Changes

New Modular Structure

• commands/ - Each command in its own module

  • exec.rs - Command execution (~75 lines)
  • ping.rs - Connectivity testing (~80 lines)
  • list.rs - Cluster listing (~50 lines)
  • upload.rs - File upload (~175 lines)
  • download.rs - File download (~240 lines)

• utils/ - Reusable utility functions

  • fs.rs - File system operations (glob, walk, format)
  • output.rs - Output file management
  • logging.rs - Logging initialization

Benefits

• Improved Maintainability: Each command is self-contained
• Better Testability: Individual modules can be tested in isolation
• Enhanced Scalability: New commands can be added without touching main.rs
• Code Reusability: Utility functions are shared across commands
• Clear Separation of Concerns: Each module has a single responsibility

Metrics

• Main.rs size: 987 → 150 lines (84% reduction)
• Average module size: ~100 lines
• Total modules created: 9 new files
• No functionality changes, only structural improvements

Test Plan

• All existing functionality preserved
• Cargo build successful
• Cargo clippy passes
• Help command works
• List command works