feat: add web interface for math exercise generator

- Create FastAPI backend with endpoints for generating math exercises
- Build Bootstrap frontend with responsive UI for exercise configuration
- Implement PDF generation functionality identical to original script
- Add README with installation and usage instructions
- Update requirements.txt with web dependencies
- Configure .gitignore to exclude compiled files and generated PDFs

.gitignore

@@ -1 +1,19 @@
 *env
+
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# Generated PDF files
+app/static/*.pdf
+
+# IDE files
+.vscode/
+.idea/
+*.swp
+*.swo
+
+# OS files
+.DS_Store
+Thumbs.db