docs: Update CHANGELOG and CONTRIBUTING for v2.0.4 refactoring

- Added v2.0.4 entry to CHANGELOG documenting the major architecture refactoring
- Updated CONTRIBUTING.md with detailed project structure documentation
- Documented all 6 refactored modules and their sub-modules
- Added guidelines for adding new features within the modular structure

Author: TexasCoding

CHANGELOG.md

@@ -13,6 +13,37 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Old implementations are removed when improved
 - Clean, modern code architecture is prioritized
 
+## [2.0.4] - 2025-08-02
+
+### Changed
+- **🏗️ Major Architecture Refactoring**: Converted all large monolithic modules into multi-file packages
+  - **client.py** → `client/` package (8 specialized modules)
+    - `rate_limiter.py`: Async rate limiting functionality
+    - `auth.py`: Authentication and token management
+    - `http.py`: HTTP client and request handling
+    - `cache.py`: Intelligent caching for instruments and market data
+    - `market_data.py`: Market data operations (instruments, bars)
+    - `trading.py`: Trading operations (positions, trades)
+    - `base.py`: Base class combining all mixins
+    - `__init__.py`: Main ProjectX class export
+  - **order_manager.py** → `order_manager/` package (10 modules)
+  - **position_manager.py** → `position_manager/` package (12 modules)  
+  - **realtime_data_manager.py** → `realtime_data_manager/` package (9 modules)
+  - **realtime.py** → `realtime/` package (8 modules)
+  - **utils.py** → `utils/` package (10 modules)
+
+### Improved
+- **📁 Code Organization**: Separated concerns into logical modules for better maintainability
+- **🚀 Developer Experience**: Easier navigation and understanding of codebase structure
+- **✅ Testing**: Improved testability with smaller, focused modules
+- **🔧 Maintainability**: Each module now has a single, clear responsibility
+
+### Technical Details
+- **Backward Compatibility**: All existing imports continue to work without changes
+- **No API Changes**: Public interfaces remain identical
+- **Import Optimization**: Reduced circular dependency risks
+- **Memory Efficiency**: Better module loading with focused imports
+
 ## [2.0.2] - 2025-08-02
 
 ### Added

CONTRIBUTING.md

@@ -174,9 +174,37 @@ Good documentation is essential for this project:
 ## Architecture Guidelines
 
 ### Project Structure
-- Maintain the existing modular architecture
-- Place new files in appropriate modules
-- Consider impacts on existing components
+
+The SDK uses a modular architecture where large components are split into multi-file packages:
+
+- **Client Module** (`client/`): Core async client functionality
+  - `auth.py`: Authentication and token management
+  - `http.py`: HTTP client and request handling
+  - `cache.py`: Caching for instruments and market data
+  - `market_data.py`: Market data operations
+  - `trading.py`: Trading operations
+  - `base.py`: Base class combining mixins
+  
+- **Trading Modules**:
+  - `order_manager/`: Order lifecycle management (10 modules)
+  - `position_manager/`: Portfolio and risk management (12 modules)
+  
+- **Real-time Modules**:
+  - `realtime/`: WebSocket client functionality (8 modules)
+  - `realtime_data_manager/`: Real-time OHLCV data (9 modules)
+  
+- **Utilities** (`utils/`): Shared utilities (10 modules)
+  - Trading calculations, portfolio analytics, pattern detection
+  - Market microstructure, formatting, environment handling
+
+- **Indicators** (`indicators/`): 58+ technical indicators
+  - Organized by category (momentum, overlap, volatility, etc.)
+
+### Adding New Features
+- Place new functionality in the appropriate existing module
+- For large features, consider creating a new sub-module
+- Maintain backward compatibility for all public APIs
+- Follow the established mixin pattern for client extensions
 
 ### Performance Considerations
 - Implement time window filtering for analysis methods