refactor roi calc js into modular files

hub/services/static/js/roi-calculator/README.md

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+# ROI Calculator Modules
+
+This directory contains the modular ROI Calculator implementation, split into focused, maintainable modules.
+
+## Module Structure
+
+### Core Modules
+
+- **`calculator-core.js`** - Main ROICalculator class with calculation logic
+- **`chart-manager.js`** - Chart.js integration and chart rendering
+- **`ui-manager.js`** - DOM updates, table rendering, and metric display
+- **`export-manager.js`** - PDF and CSV export functionality
+- **`input-utils.js`** - Input validation, parsing, and formatting utilities
+- **`roi-calculator-app.js`** - Main application coordinator class
+
+### Integration
+
+- **`../roi-calculator-modular.js`** - Global function wrappers for backward compatibility
+
+## Key Improvements
+
+1. **Modular Architecture**: Each module has a single responsibility
+2. **Error Handling**: Comprehensive try-catch blocks with graceful fallbacks
+3. **No Global Variables**: App instance contained in window.ROICalculatorApp
+4. **Type Safety**: Input validation and null checks throughout
+5. **Separation of Concerns**: Calculation, UI, charts, and exports are separated
+
+## Usage
+
+All modules are automatically loaded via the HTML template. The ROICalculatorApp class coordinates all modules and provides the same public API as the original monolithic version.
+
+## Backward Compatibility
+
+All existing HTML onclick handlers and function calls continue to work through the global wrapper functions in `roi-calculator-modular.js`.