feat: add billing page and subscription plans, integrate Stripe for upgrades

docs: add README and gitignore configuration

feat: set up Express server with database schema

feat: implement main App component with routing and auth guards

feat: create optimization page for prompt enhancement

feat: build dashboard page with prompt management

feat: implement login page with Google authentication

feat: create navigation bar component with auth integration

feat: add API service layer for backend communication

feat: implement authentication context provider

feat: integrate Firebase authentication and configuration

assets: add static assets and resources

feat: set up React app entry point and base styles

feat: add HTML entry point and public assets

config: add build tooling and linting configuration