feat: initialize monorepo with full dev team best practices

- Unified monorepo with backend (Express), frontend (Next.js), and devops
- Backend: ESLint, Prettier, Jest tests (3 passing), health endpoint, .env.example
- Frontend: Fixed build errors, fixed all lint errors (0 remaining), tests passing
- DevOps: Docker Compose with PostgreSQL, backend, frontend + healthchecks
- CI/CD: 3 GitHub Actions workflows (backend, frontend, docker integration)
- DX: Husky pre-commit hooks with smart change detection
- Docs: Root README with architecture, CONTRIBUTING.md, PR template

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

CONTRIBUTING.md

@@ -0,0 +1,87 @@
+# Contributing to Website Monitoring
+
+## Branch Strategy
+
+```
+main          ← production-ready, protected
+  └─ develop  ← integration branch
+       └─ feature/xxx  ← your work
+       └─ fix/xxx      ← bug fixes
+       └─ chore/xxx    ← maintenance
+```
+
+### Rules
+- **Never push directly to `main`** — always open a PR
+- Branch from `develop` for features, from `main` for hotfixes
+- Delete branches after merge
+
+## Development Setup
+
+```bash
+# Clone & install
+git clone <repo-url>
+cd website-monitoring
+npm install
+
+# Install project dependencies
+cd website-monitoring-backend && npm install && cd ..
+cd website-monitoring-frontend && npm install && cd ..
+
+# Start everything
+npm run dev
+```
+
+## Workflow
+
+1. **Create a branch**: `git checkout -b feature/my-feature develop`
+2. **Make changes**: Write code, add tests
+3. **Verify locally**:
+   ```bash
+   npm run lint        # No errors
+   npm run test        # All pass
+   npm run build       # Compiles clean
+   ```
+4. **Commit**: Use [Conventional Commits](https://www.conventionalcommits.org/)
+   ```
+   feat: add uptime monitoring endpoint
+   fix: resolve SSE connection leak
+   chore: update lighthouse dependency
+   docs: add API endpoint documentation
+   test: add lighthouse service unit tests
+   ```
+5. **Push & open PR**: Target `develop` (or `main` for hotfixes)
+
+## Code Review Checklist
+
+- [ ] Code compiles and all tests pass
+- [ ] New code has tests
+- [ ] No `console.log` left in production code (use proper logger)
+- [ ] TypeScript types are explicit (minimize `any`)
+- [ ] API changes are documented
+- [ ] Environment variables documented in `.env.example`
+- [ ] No secrets committed
+
+## Code Style
+
+- **TypeScript** everywhere (no plain JS)
+- **ESLint** for linting — `npm run lint`
+- **Prettier** for formatting — auto-runs on commit via Husky
+- Use `async/await` over `.then()` chains
+- Prefer named exports over default exports
+
+## Testing
+
+- **Backend**: Jest + Supertest — `cd website-monitoring-backend && npm test`
+- **Frontend**: Jest + Testing Library — `cd website-monitoring-frontend && npm test`
+- Aim for tests on all API endpoints and critical business logic
+- Use meaningful test names: `it("should return 400 when URL is missing")`
+
+## Docker
+
+```bash
+# Full stack with Docker Compose
+npm run docker:up
+
+# Tear down
+npm run docker:down
+```