feat: Add color support to statistics and show commands

[biwakonbu]

Summary

Add color support to statistics and show commands to improve readability and user experience.

Motivation

Currently, statistics and show commands output plain text which can be difficult to scan quickly. Adding colors would help users identify:

• Status types (done=green, doing=yellow, todo=blue, pending=orange, cancelled=red)
• Priority levels (critical=red, high=orange, medium=yellow, low=gray)
• Different sections and headers

Acceptance Criteria

• Add color library dependency (e.g., fatih/color or similar)
• Colorize status indicators in statistics output
• Colorize priority levels in task displays
• Colorize section headers and separators
• Add --no-color flag to disable colors for CI/scripting
• Respect NO_COLOR environment variable
• Ensure colors work across different terminals

Implementation Notes

• Use ANSI color codes that work on most terminals
• Consider terminal capabilities detection
• Maintain backward compatibility with plain text output
• Test on various terminal environments

Examples

📊 Task Statistics for Branch 'feature/auth'

Status Summary:
  ✅ Done: 2 (green)
  🔄 Doing: 1 (yellow) 
  📋 Todo: 3 (blue)
  ⏸️ Pending: 0 (orange)
  ❌ Cancelled: 0 (red)

Labels

enhancement, user-experience