Add localization support and docs

docs/2025-10-18_MODULAR_STRUCTURE.md

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+# Medication Plan Assistant - Modular Structure
+
+This application has been successfully modularized to simplify maintenance and further development.
+
+## 📁 New Project Structure
+
+```text
+src/
+├── App.js                     # Main component (greatly simplified)
+├── components/                # UI components
+│   ├── DoseSchedule.js        # Dosage schedule input
+│   ├── DeviationList.js       # Deviations from the schedule
+│   ├── SuggestionPanel.js     # Correction suggestions
+│   ├── SimulationChart.js     # Chart component
+│   ├── Settings.js            # Settings panel
+│   ├── TimeInput.js           # Time input with picker
+│   └── NumericInput.js        # Numeric input with +/- buttons
+├── hooks/                     # Custom React hooks
+│   ├── useAppState.js         # State management & local storage
+│   └── useSimulation.js       # Simulation logic & calculations
+├── utils/                     # Utility functions
+│   ├── timeUtils.js           # Time utility functions
+│   ├── pharmacokinetics.js    # PK calculations
+│   ├── calculations.js        # Concentration calculations
+│   └── suggestions.js         # Correction suggestion algorithm
+└── constants/
+    └── defaults.js            # Constants & default values
+```
+
+## 🎯 Advantages of the new structure
+
+### ✅ Better maintainability
+
+- **Small, focused modules**: Each file has a clear responsibility
+- **Easier debugging**: Problems can be localized more quickly
+- **Clearer code organization**: Related functions are grouped together
+
+### ✅ Reusability
+
+- **UI components**: `TimeInput`, `NumericInput` can be used anywhere
+- **Utility functions**: PK calculations are isolated and testable
+- **Custom hooks**: State logic is reusable
+
+### ✅ Development friendliness
+
+- **Parallel development**: Teams can work on different modules
+- **Simpler testing**: Each module can be tested in isolation
+- **Better IDE support**: Smaller files = better performance
+
+### ✅ Scalability
+
+- **New features**: Easy to add as new modules
+- **Code splitting**: Possible for better performance
+- **Refactoring**: Changes are limited locally
+
+## 🔧 Technical details
+
+### State management
+
+- **useAppState**: Manages global app state and LocalStorage
+- **useSimulation**: Manages all simulation-related calculations
+
+### Component architecture
+
+- **Dumb components**: UI components receive props and call callbacks
+- **Smart Components**: Hooks manage state and business logic
+- **Separation of Concerns**: UI, state, and business logic are separated
+
+### Utils & Calculations
+
+- **Pure functions**: All calculations are side-effect-free
+- **Modular exports**: Functions can be imported individually
+- **Typed interfaces**: Clear input/output definitions
+
+## 🚀 Migration complete
+
+The application works identically to the original version, but now:
+
+- Split into **350+ lines** across **several small modules**
+- **Easier to understand** and modify
+- **Ready for further features** and improvements
+- **More test-friendly** for unit and integration tests