feat: implement user-configurable key mappings

[jellydn]

Custom keymap

Summary

This PR implements user-configurable key mappings to address multiple keyboard-related issues, allowing users to customize key bindings according to their preferences and resolve terminal compatibility problems.

Closes #154, #119, #57

Issues Addressed

Issue #154: "Have re-mappable keys"

• ✅ Implemented: Complete user-configurable key mapping system
• ✅ Smart Merging: Users only specify keys they want to customize
• ✅ Backward Compatible: Default mappings match original hardcoded values

Issue #119: "Modify Key Binding for Detach Session Action"

• ✅ Root Cause: Users want to customize key bindings, particularly for problematic keys in WSL
• ✅ Solution: Now users can customize any key binding, including quit/detach actions
• ✅ Example: "quit": ["q", "Q", "esc"] gives multiple safe alternatives

Issue #57: "ctrl-q doesn't work in vscode/cursor terminal"

• ✅ Root Cause: Terminal compatibility issues with ctrl key combinations
• ✅ Solution: Users can now avoid problematic ctrl keys entirely
• ✅ Safe Alternatives: Documentation provides guidance on terminal-safe key combinations

Implementation

Core Features

• Dynamic Key Mapping: Each action supports single or multiple key alternatives
• Partial Configuration: Users only specify keys they want to change
• Safe Defaults: Avoids terminal signal conflicts (ctrl+c, ctrl+d)
• Flexible Syntax: Supports uppercase, shift combinations, and special keys

Configuration Example

{
  "key_mappings": {
    "quit": ["q", "Q", "esc"],          // Multiple safe alternatives for #119/#57
    "checkout": ["C"],                   // Single alternative
    "submit": ["P", "shift+s"]           // Multiple options for flexibility
  }
}

Terminal Compatibility Solutions

• Issue ctrl-q doesn't work in vscode/cursor terminal #57 (ctrl-q): Users can now map quit to ["q", "Q", "esc"] instead of relying on ctrl+q
• Issue Modify Key Binding for Detach Session Action #119 (WSL problems): Users can customize detach/quit keys to avoid terminal conflicts
• Documentation: Clear guidance on avoiding problematic key combinations

Benefits

For Issue #154 (Re-mappable keys)

• Complete key customization system
• Maintains backward compatibility
• Intuitive configuration format

For Issue #119 (Detach session key binding)

• Users can now customize quit/detach keys freely
• Multiple alternatives prevent terminal conflicts
• Works reliably across different terminal environments

For Issue #57 (ctrl-q terminal issues)

• Eliminates dependency on ctrl combinations
• Provides multiple safe alternatives
• Resolves vscode/cursor terminal compatibility

Testing

• ✅ Builds successfully with go build
• ✅ All existing tests pass
• ✅ Comprehensive Makefile for testing different scenarios
• ✅ Verified terminal compatibility improvements
• ✅ Backward compatibility maintained

Documentation

• KEY_CUSTOMIZATION.md: Complete user guide with examples
• Terminal safety warnings and best practices
• Multiple configuration examples for different use cases
• Makefile targets for easy testing and verification

Files Changed

• config/config.go: Added KeyMappings field and merging logic
• keys/keys.go: Implemented configurable key system
• app/app.go: Added key mapping initialization
• KEY_CUSTOMIZATION.md: User documentation
• example-config.json: Safe key combination examples
• Makefile: Development and testing workflow

This implementation provides a comprehensive solution to all keyboard-related issues while maintaining simplicity and backward compatibility.