refactor: flatten monorepo structure to backend/ frontend/ devops/

Rename subdirectories for a cleaner single-repo layout:
- website-monitoring-backend/  → backend/
- website-monitoring-frontend/ → frontend/
- website-monitoring-devops/   → devops/

Update all references in package.json scripts, CI workflows,
docker-compose, pre-commit hooks, and documentation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/README.md

@@ -0,0 +1,57 @@
+# Website Monitoring Backend
+
+Express.js API server that runs Google Lighthouse audits on websites and streams real-time progress via Server-Sent Events.
+
+## Tech Stack
+
+- **Runtime**: Node.js 18+
+- **Framework**: Express.js
+- **Language**: TypeScript
+- **Auditing**: Google Lighthouse + Chrome Headless
+- **Database**: PostgreSQL (via `pg`)
+
+## Quick Start
+
+```bash
+cp .env.example .env
+npm install
+npm run build
+npm start
+```
+
+## Scripts
+
+| Script | Description |
+|--------|-------------|
+| `npm run build` | Compile TypeScript to `dist/` |
+| `npm start` | Run the production server |
+| `npm run dev` | Watch mode for development |
+| `npm test` | Run Jest tests |
+| `npm run test:coverage` | Run tests with coverage report |
+| `npm run lint` | Run ESLint |
+| `npm run format` | Format code with Prettier |
+
+## API Endpoints
+
+| Method | Path | Description |
+|--------|------|-------------|
+| `GET` | `/` | API info |
+| `GET` | `/health` | Health check |
+| `POST` | `/api/lighthouse` | Start Lighthouse audit (body: `{ "url": "https://example.com" }`) |
+| `GET` | `/api/lighthouse/status/:id` | SSE stream for audit progress |
+
+## Environment Variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `PORT` | `5000` | Server port |
+| `DATABASE_URL` | — | PostgreSQL connection string |
+| `CORS_ORIGIN` | `*` | Allowed CORS origin |
+| `CHROME_PATH` | — | Path to Chrome binary (Docker) |
+
+## Docker
+
+```bash
+docker build -t website-monitoring-backend .
+docker run -p 5000:5000 website-monitoring-backend
+```