chore: initial project setup with backend, frontend, and infrastructure

Add complete NexaPantry application structure including:
- Docker Compose configuration with PostgreSQL, Redis, FastAPI backend, worker, frontend and Caddy
- Environment configuration template with database, auth, and service settings
- GitHub Actions CI workflow for backend/frontend linting, testing, auditing and Docker builds
- AGPL-3.0 license and comprehensive README with setup, development, and security documentation
- Backend

frontend/src/App.test.tsx

@@ -0,0 +1,8 @@
+import { render, screen } from '@testing-library/react';
+import App from './App';
+
+test('renders loading shell', () => {
+  render(<App />);
+  expect(screen.getByText('NexaPantry')).toBeInTheDocument();
+});
+