Глобальный рефакторинг - Global code quality improvements

[konard]

🔧 Global Refactoring

This PR implements comprehensive code quality improvements across all components of the GPTutor project as requested in issue #208.

🚀 Backend Improvements (Spring Boot/Java)

• Constructor Injection: Replaced @Autowired field injection with constructor injection in all controllers for better testability and immutability
  • ConversationController: Improved dependency injection pattern
  • ImagesController: Refactored to use constructor injection with multiple services
  • HistoryController: Enhanced with proper dependency management
• Dependency Management: Removed redundant Spring Boot version declarations in pom.xml to rely on parent BOM
• Type Safety: Improved type handling and removed unsafe generic casting

🐍 Python Models Service

• Error Handling: Implemented comprehensive try-catch blocks with proper error responses
• Request Validation: Added validation for required JSON fields and proper HTTP status codes
• Logging: Integrated structured logging with traceback information for debugging
• API Standards: Consistent JSON responses and proper HTTP status codes

🔍 RAG Service (TypeScript/Node.js)

• Type Safety: Added proper TypeScript interfaces and type guards
• Error Handling: Comprehensive error handling with structured error responses
• Environment Validation: Added validation for required environment variables
• API Improvements: Added health endpoint and improved request validation
• Code Organization: Better function organization and documentation

🎨 Frontend Improvements (React/TypeScript)

• Import Organization: Restructured imports in App.tsx with logical grouping and documentation:
  • External libraries first
  • Styles section
  • Core entities and services
  • Components grouped by functionality (panels, modals, etc.)
• Better Maintainability: Clear separation of concerns in import statements

📋 Quality Standards Applied

• ✅ Dependency injection best practices
• ✅ Proper error handling and validation
• ✅ Type safety improvements
• ✅ Code organization and readability
• ✅ Consistent coding patterns
• ✅ Removal of code duplication
• ✅ Enhanced maintainability

🧪 Testing Recommendations

• Backend controllers can now be easily unit tested due to constructor injection
• Python services have proper error boundaries for integration testing
• RAG service includes health check endpoint for monitoring

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Fixes #208

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