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

packages/shared/ww_shared/envelope.py

@@ -0,0 +1,16 @@
+"""统一错误信封（ARCH §7.1）——带 request_id 以便端到端 grep。"""
+
+from __future__ import annotations
+
+from pydantic import BaseModel, Field
+
+
+class ErrorBody(BaseModel):
+    code: str
+    message: str
+    details: dict[str, object] = Field(default_factory=dict)
+    request_id: str | None = None
+
+
+class ErrorEnvelope(BaseModel):
+    error: ErrorBody