Add DeepSeek AI as a new search engine option with API key management

[Copilot]

🚀 New Feature: DeepSeek AI Integration

This PR adds DeepSeek AI as a new search engine option to Codelf, providing AI-powered code suggestions and variable naming alongside the existing SearchCode.com functionality.

✨ Features Added

🔍 Dual Search Engine Support

• SearchCode: Real-world code from GitHub, GitLab, BitBucket (existing, default)
• DeepSeek AI: AI-powered variable naming and code suggestions (new)

🔑 Flexible API Key Management

• Optional API key configuration via settings modal
• Secure browser-only storage (localStorage) - never sent to Codelf servers
• Fallback to demo mode with mock results when no API key provided
• Clear privacy notices and user control

🎨 Seamless UI Integration

• New search engine selector dropdown in main interface
• Settings button for DeepSeek configuration when selected
• Maintains consistent design with existing components
• Responsive design support

🛠 Implementation Details

New Components

• DeepSeekSearchData: Service class for API integration with caching and error handling
• SearchEngineSelector: React component for engine selection with settings modal

Enhanced Components

• SearchCodeModel: Updated to route requests between different search engines
• SearchBar: Integrated search engine selector
• MainContainer: Added search engine change handling

📊 Usage Example

// Users can now select DeepSeek AI from the dropdown
// and optionally configure their API key for enhanced results

// Example search flow:
1. Select "DeepSeek AI" from search engine dropdown
2. Optionally click settings ⚙️ to configure API key
3. Search for "user authentication" 
4. Get AI-generated variable names and patterns

🔧 API Integration

• Endpoint: https://api.deepseek.com/chat/completions
• Authentication: Bearer token (user's API key)
• Fallback: Demo mode with mock results when no API key
• Caching: Session-based result caching for performance
• Error Handling: Graceful fallback on API failures

🔒 Privacy & Security

• API keys stored only in user's browser (localStorage)
• Never transmitted to Codelf servers
• User can clear API key anytime
• Transparent about data usage
• No cross-engine data sharing

📱 User Interface

Search Engine: [DeepSeek AI ▼] [⚙️ Settings]
┌─────────────────────────────────┐
│ Search Input Field              │
│ [🔍] [Language Filter ▼]       │
└─────────────────────────────────┘

Settings Modal:

🧠 DeepSeek AI Settings
┌─────────────────────────────────┐
│ API Key (Optional)              │
│ [••••••••••••••••••••] [👁️]    │
│                                 │
│ ℹ️ Privacy Notice: API key is   │
│   stored locally in browser     │
│                                 │
│ [Clear Key] [Cancel] [Save]     │
└─────────────────────────────────┘

🧪 Testing

• ✅ API key storage/retrieval functionality
• ✅ Search result parsing and display
• ✅ Error handling and fallback scenarios
• ✅ UI component rendering and interactions
• ✅ Backward compatibility with existing SearchCode functionality

📈 Impact

• No Breaking Changes: Full backward compatibility maintained
• Zero New Dependencies: Uses existing React/Semantic UI components
• Minimal Code Changes: 611 lines added, 11 removed across 7 files
• Enhanced User Experience: More search options and AI-powered suggestions

🌟 Benefits

1. More Options: Users can choose between real-world code examples and AI suggestions
2. Flexibility: Works with or without API key
3. Privacy-First: User controls all data and API key storage
4. Performance: Built-in caching and error handling
5. Extensible: Easy to add more AI providers in the future

This enhancement maintains Codelf's core mission of helping developers find better variable names while adding the power of modern AI assistance.

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