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>

.github/pull_request_template.md

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+## Description
+
+<!-- What does this PR do? Link to issue if applicable. -->
+
+Closes #
+
+## Type of Change
+
+- [ ] 🐛 Bug fix (non-breaking change fixing an issue)
+- [ ] ✨ New feature (non-breaking change adding functionality)
+- [ ] 💥 Breaking change (fix or feature causing existing functionality to change)
+- [ ] 📝 Documentation update
+- [ ] 🧹 Chore (dependency update, refactor, etc.)
+
+## Changes Made
+
+<!-- List the key changes -->
+
+-
+-
+-
+
+## Testing
+
+- [ ] Existing tests pass (`npm test`)
+- [ ] New tests added for new functionality
+- [ ] Tested locally with `npm run dev`
+- [ ] Tested with Docker (`npm run docker:up`)
+
+## Checklist
+
+- [ ] My code follows the project code style
+- [ ] I've run `npm run lint` with no errors
+- [ ] I've updated documentation if needed
+- [ ] I've updated `.env.example` if new env vars were added
+- [ ] No secrets or credentials in the code
+
+## Screenshots (if applicable)
+
+<!-- Add screenshots for UI changes -->