feat: Phase 0 — monorepo 骨架 + 全表迁移 + FastAPI/Next 骨架 + CI

- uv(workspace) + pnpm monorepo；docker-compose(pg+api+web)
- SQLAlchemy 16 MVP 表 + Alembic 初版迁移(无漂移，users stub)
- FastAPI 骨架：统一错误信封(带 request_id) + structlog + /jobs/:id + OpenAPI
- Next.js 骨架：纸感主题 token + OpenAPI→TS 客户端代码生成(gen:api)
- CI(ruff/mypy/pytest + pg service + alembic 漂移校验)
- 四份设计规格(PRODUCT/UX/ARCHITECTURE/DEV_PLAN) + CLAUDE.md

tests/test_error_envelope.py

@@ -0,0 +1,17 @@
+from __future__ import annotations
+
+from ww_shared import AppError, ErrorBody, ErrorCode, ErrorEnvelope
+
+
+def test_app_error_maps_to_http_status() -> None:
+    assert AppError(ErrorCode.NOT_FOUND, "x").http_status == 404
+    assert AppError(ErrorCode.CONFLICT_UNRESOLVED, "x").http_status == 409
+
+
+def test_envelope_serializes_with_request_id() -> None:
+    env = ErrorEnvelope(
+        error=ErrorBody(code=ErrorCode.VALIDATION, message="bad", request_id="rid-1")
+    )
+    dumped = env.model_dump()
+    assert dumped["error"]["code"] == "VALIDATION"
+    assert dumped["error"]["request_id"] == "rid-1"