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>

package.json

@@ -0,0 +1,22 @@
+{
+  "name": "retail-media-calculator",
+  "version": "1.0.0",
+  "description": "Retail Media Business Case Calculation Agent",
+  "main": "server.js",
+  "scripts": {
+    "start": "node server.js",
+    "dev": "nodemon server.js"
+  },
+  "dependencies": {
+    "body-parser": "^1.20.2",
+    "exceljs": "^4.4.0",
+    "express": "^4.18.2",
+    "fs-extra": "^11.3.1",
+    "node-xlsx": "^0.24.0",
+    "python-shell": "^5.0.0",
+    "xlsx": "^0.18.5"
+  },
+  "devDependencies": {
+    "nodemon": "^3.0.1"
+  }
+}