refactor: simplificar flujo de usuario

[AlexisAyalaS]

🔧 feat: Add real AI API integration with smart fallback system

📝 Description

This PR implements real AI API integration for ChatGPT, DeepSeek, and Gemini platforms, replacing the previous simulated responses. The system includes a smart fallback mechanism that uses clipboard and browser when API keys are not available.

🔧 Technical Implementation

Real API Integration

• OpenAI ChatGPT: Uses official OpenAI API with GPT-3.5-turbo
• DeepSeek: Integrates with DeepSeek Chat API
• Google Gemini: Connects to Gemini Pro via Google AI Studio API
• Proper error handling with fallback to clipboard system

Smart Fallback System

• Clipboard integration: Automatically copies prompts when API keys are missing
• Browser automation: Opens corresponding AI chat platforms
• User instructions: Clear guidance for manual prompt usage
• Multiple process fallback: Combined prompts for batch operations

Dynamic Menu System

• API key detection: Automatically detects configured API keys
• Adaptive options: Shows/hides multiple processes based on API availability
• Placeholder validation: Prevents using example API keys from env.example

Enhanced Configuration

• Environment variables: Proper .env file support with dotenv
• Node.js v18+ requirement: Updated engine requirements for all dependencies
• API key validation: Checks for valid, non-placeholder keys

🎬 Demo

With API Keys

# Configure API keys in .env
OPENAI_API_KEY=sk-your-real-key
DEEPSEEK_API_KEY=sk-your-real-key  
GEMINI_API_KEY=your-real-key

# Use all features including multiple processes
git-ai
# Select: 🔄 Perform multiple processes
# Result: Direct AI responses via API

Without API Keys

# No API keys configured
git-ai
# Select: 📝 Generate Pull Request message  
# Result: Prompt copied to clipboard + browser opens
# Instructions: Paste in AI chat and copy response

Smart Menu Adaptation

🎯 What process do you want to perform?

✅ Available with API keys:
  🔄 Perform multiple processes
  📝 Generate Pull Request message
  💬 Suggest commit message
  🌿 Suggest branch name

⚠️ Available without API keys (clipboard fallback):
  📝 Generate Pull Request message  
  💬 Suggest commit message
  🌿 Suggest branch name

📋 Changes Made

Core Features

• Added real API calls to OpenAI, DeepSeek, and Gemini
• Implemented smart fallback system for missing API keys
• Created dynamic menu that adapts to available API keys
• Added clipboard integration for manual AI usage
• Enhanced error handling with graceful degradation

Configuration Updates

• Updated README with comprehensive API setup instructions
• Added environment variable validation
• Increased Node.js requirement to v18+ for compatibility
• Improved documentation for fallback system

Technical Improvements

• Added proper API response formatting
• Implemented branch name extraction from AI responses
• Enhanced multiple process handling with combined prompts
• Added platform availability detection

The system now provides a seamless experience whether users have API keys configured or prefer manual interaction with AI platforms.