feat: add frontend-architect and backend-developer agent roles (#1)

* feat: add frontend-architect and backend-developer agent roles

- Frontend Architect: UI architecture, design systems, component strategy, build pipelines
- Backend Developer: API implementation, business logic, database queries, service integration

Requested to replace generic senior-developer mappings with role-specific specialists.

* docs: add frontend-architect and backend-developer to README roster

README.md

@@ -73,7 +73,9 @@ Building the future, one commit at a time.
 | Agent | Specialty | When to Use |
 |-------|-----------|-------------|
 | 🎨 [Frontend Developer](engineering/engineering-frontend-developer.md) | React/Vue/Angular, UI implementation, performance | Modern web apps, pixel-perfect UIs, Core Web Vitals optimization |
+| 🏛️ [Frontend Architect](engineering/engineering-frontend-architect.md) | UI architecture, design systems, build pipelines, cross-team standards | Frontend system design, component library strategy, monorepo architecture |
 | 🏗️ [Backend Architect](engineering/engineering-backend-architect.md) | API design, database architecture, scalability | Server-side systems, microservices, cloud infrastructure |
+| ⚙️ [Backend Developer](engineering/engineering-backend-developer.md) | API implementation, business logic, database queries, service integration | Feature implementation, endpoint delivery, production-ready server-side code |
 | 📱 [Mobile App Builder](engineering/engineering-mobile-app-builder.md) | iOS/Android, React Native, Flutter | Native and cross-platform mobile applications |
 | 🤖 [AI Engineer](engineering/engineering-ai-engineer.md) | ML models, deployment, AI integration | Machine learning features, data pipelines, AI-powered apps |
 | 🚀 [DevOps Automator](engineering/engineering-devops-automator.md) | CI/CD, infrastructure automation, cloud ops | Pipeline development, deployment automation, monitoring |