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

apps/api/ww_api/main.py

@@ -0,0 +1,55 @@
+"""FastAPI 应用入口（ARCH §7）。"""
+
+from __future__ import annotations
+
+from collections.abc import AsyncIterator
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI, Request
+from fastapi.responses import JSONResponse
+from ww_db import get_sessionmaker
+from ww_shared import AppError, ErrorBody, ErrorEnvelope
+
+from ww_api.logging_config import configure_logging, get_logger
+from ww_api.middleware import request_id_middleware
+from ww_api.routers import health, jobs, projects, settings_providers
+from ww_api.services.project_deps import seed_stub_user
+
+configure_logging()
+log = get_logger("ww.api")
+
+
+@asynccontextmanager
+async def _lifespan(app: FastAPI) -> AsyncIterator[None]:
+    # 幂等 seed 单用户 stub——所有 owner_id FK 依赖它（见 memory/gotchas）。
+    async with get_sessionmaker()() as session:
+        await seed_stub_user(session)
+    yield
+
+
+def create_app() -> FastAPI:
+    app = FastAPI(title="网文创作工作流 API", version="0.0.0", lifespan=_lifespan)
+    app.middleware("http")(request_id_middleware)
+
+    @app.exception_handler(AppError)
+    async def _app_error_handler(request: Request, exc: AppError) -> JSONResponse:
+        request_id = getattr(request.state, "request_id", None)
+        log.warning("app_error", code=exc.code, message=exc.message)
+        envelope = ErrorEnvelope(
+            error=ErrorBody(
+                code=exc.code,
+                message=exc.message,
+                details=exc.details,
+                request_id=request_id,
+            )
+        )
+        return JSONResponse(status_code=exc.http_status, content=envelope.model_dump())
+
+    app.include_router(health.router)
+    app.include_router(jobs.router)
+    app.include_router(projects.router)
+    app.include_router(settings_providers.router)
+    return app
+
+
+app = create_app()