Add xlsxwriter-based Excel generation scripts with openpyxl implementation

- Created create_excel_xlsxwriter.py and update_excel_xlsxwriter.py
- Uses openpyxl exclusively to preserve Excel formatting and formulas
- Updated server.js to use new xlsxwriter scripts for form submissions
- Maintains all original functionality while ensuring proper Excel file handling

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

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+# Retail Media Business Case Calculator
+
+This application helps retail media professionals generate business cases by collecting key metrics and calculating potential reach and impressions across different channels.
+
+## Features
+
+- Clean, user-friendly form for collecting retail media data
+- Automatic calculation of key metrics:
+  - Potential reach in-store (digital screens and radio)
+  - Unique impressions in-store
+  - Potential reach on-site
+  - Unique impressions on-site
+  - Potential reach off-site
+  - Unique impressions off-site
+- Results saved to a JSON file for reporting
+- Thank you page with confirmation message
+
+## Installation
+
+1. Clone the repository
+2. Install dependencies:
+
+```bash
+npm install
+```
+
+## Running the Application
+
+Start the server:
+
+```bash
+npm start
+```
+
+For development with auto-restart:
+
+```bash
+npm run dev
+```
+
+The application will be available at http://localhost:3000
+
+## Project Structure
+
+- `index.html` - Main form interface for collecting user data
+- `thank-you.html` - Confirmation page after form submission
+- `server.js` - Express server handling form submissions and routing
+- `index.js` - Business logic for calculating retail media metrics
+- `config.json` - Configuration file with constants and coefficients
+- `results.json` - Output file where calculation results are stored
+- `public/` - Static assets directory
+
+## How It Works
+
+1. Users fill out the business case form with their retail media data
+2. The form validates input and submits data to the server
+3. Server processes the data using formulas in `index.js`
+4. Results are saved to `results.json` and user is redirected to thank-you page
+5. Retail media specialists follow up with the user with a customized business case
+
+## Technologies Used
+
+- Node.js and Express for the backend
+- HTML/CSS/JavaScript for the frontend
+- TailwindCSS for styling
+- Vanilla JavaScript for form validation and interactions
+
+## Configuration
+
+The application uses a `config.json` file that contains constants and coefficients for the formulas. You can modify these values to adjust the calculation logic.
+
+## Development Notes
+
+- Form styling uses a clean white design with accent colors
+- Form validation ensures complete and accurate data collection
+- The server includes error handling for form submissions
+- Calculations are based on industry-standard formulas for retail media