Add sensor storefront UI, admin inventory panel, and lightweight Node API

[sandip444]

Motivation

• Implement a sensor-focused e-commerce demo with a React frontend and a simple Node.js backend to provide an admin inventory management area and a customer-facing shop view.
• Provide a resilient developer experience by adding a local API and a frontend fallback dataset so the UI works even when the backend is unreachable.

Description

• Add a lightweight Express API at server/index.js with endpoints GET /api/products, GET /api/products/:id, POST /api/products, PUT /api/products/:id, and DELETE /api/products/:id, and include server/package.json to run the service.
• Build the storefront UI and routing in React including the home inventory page (/), product detail view (/product/:productId), and a new admin inventory panel (/admin) with src/Containers/AdminPanel.jsx, updated src/App.js, and src/Containers/* components and styles in src/App.css.
• Add a frontend API helper src/api.js and sample fallback data src/data/sampleProducts.js and wire fallbacks into productListing, prodectDetails, and AdminPanel so the app loads sample inventory when the API is unavailable.
• Update the README with backend instructions and include improved header/navigation and product card/detail UI changes.

Testing

• Ran the frontend with npm start and the development server compiled successfully and served the app at http://localhost:3000 (webpack compiled successfully).
• Captured a smoke screenshot using a Playwright script which produced an artifact artifacts/sensor-shop-home.png confirming the UI rendered.
• Attempted cd server && npm install to install backend dependencies but the install failed with an npm 403 error, so the server was not started in this environment.

---

Codex Task