feat: add staged local-first pipeline foundations

[ComBba]

What

• add a staged, contract-first pipeline path behind VIBEDEPLOY_USE_STAGED_PIPELINE
• freeze machine-parseable OpenAPI JSON before code generation
• inject deterministic scaffold/types/pydantic/design context before monolithic codegen
• block deploy unless contract/build/runtime gates pass locally
• document the local-first execution model

Why

The current pipeline jumps from blueprint to code generation, which allows frontend/backend contract drift and static mockups. This slice makes the contract a first-class artifact and introduces hard local gates before deploy.

Included

• api_contract_generator_node
• spec_freeze_gate
• scaffold_generator_node
• type_generator_node
• pydantic_generator_node
• design_system_generator
• contract_validator_node
• wiring_validator
• local_runtime_validator
• deploy_gate
• staged graph topology in agent/graph.py
• state schema extensions
• focused tests + local-first doc

Verification

• cd agent && pytest tests/test_staged_pipeline_nodes.py tests/test_contract_validator.py tests/test_build_validator.py -q
• cd agent && ruff check graph.py state.py nodes/api_contract_generator.py nodes/scaffold_generator.py nodes/type_generator.py nodes/pydantic_generator.py nodes/spec_freeze_gate.py nodes/design_system_generator.py nodes/wiring_validator.py nodes/local_runtime_validator.py nodes/deploy_gate.py nodes/contract_validator.py tests/test_staged_pipeline_nodes.py
• VIBEDEPLOY_USE_STAGED_PIPELINE=true python -c \"from agent.graph import create_graph; print(type(create_graph()).__name__)\"

Notes

• legacy graph remains default; staged path is opt-in via feature flag
• this is the first slice, not the final full per-file generation rewrite

Summary by CodeRabbit

릴리스 노트

• New Features

  • 환경 변수로 활성화되는 단계별(staged) 파이프라인 추가
  • API 계약 생성·검증, 스펙 동결 절차 및 배선 검증 추가
  • 스캐폴딩 분리된 프론트/백엔드 생성, TypeScript 타입·클라이언트 및 Pydantic 모델 자동 생성
  • 로컬 런타임 검증과 배포 게이트로 배포 준비 판단
  • 파일별 LLM 기반 코드 생성 옵션과 디자인 시스템 생성 지원

• Documentation

  • 로컬 우선 단계별 파이프라인 운영 가이드 추가

• Tests

  • 단계별 파이프라인 및 노드 통합 테스트 추가 및 확장