请创建以下 3 个文件。backend 目录已存在，但 backend/app/ 需要新建。

## 文件 1: backend/app/__init__.py
空文件。

## 文件 2: backend/app/config.py
```python
"""应用配置 — 从环境变量 / .env 读取。"""
from pydantic_settings import BaseSettings


class Settings(BaseSettings):
    database_url: str = "postgresql+asyncpg://hive_admin:changeme@localhost:5432/hive_manage_v3"
    jwt_secret: str = "change-me"
    jwt_algorithm: str = "HS256"
    jwt_expire_minutes: int = 1440
    hermes_cli_path: str = "/home/enzo/.local/bin/hermes"
    hermes_profiles_root: str = "/home/enzo/.hermes/profiles"
    admin_email: str = "admin@zhiwei.local"
    admin_password: str = "admin123"

    model_config = {"env_file": ".env"}


settings = Settings()
```

## 文件 3: backend/app/database.py
```python
"""异步 SQLAlchemy 引擎 + session 工厂。"""
from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession
from sqlalchemy.orm import DeclarativeBase

from app.config import settings

engine = create_async_engine(settings.database_url, echo=False)
async_session = async_sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)


class Base(DeclarativeBase):
    pass


async def get_db() -> AsyncSession:
    async with async_session() as session:
        yield session
```

## 文件 4: backend/app/main.py
```python
"""FastAPI 应用入口。"""
from contextlib import asynccontextmanager
from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware

from app.database import engine, Base


@asynccontextmanager
async def lifespan(app: FastAPI):
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)
    yield
    await engine.dispose()


app = FastAPI(
    title="Hive Manage v3",
    version="0.1.0",
    lifespan=lifespan,
)

app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)


@app.get("/api/v1/health")
async def health_check():
    return {"status": "ok"}
```

创建完成后，执行以下验证：
1. `cat` 检查每个文件内容
2. `cd backend && pip install -e ".[dev]"` 安装依赖
3. `cd backend && python -c "from app.main import app; print('FastAPI app created OK')"` 验证导入
4. git add + git commit -m "feat: FastAPI skeleton with config, database, health endpoint"