feat(工作日): 新增工作小时计算工具 + 节假日表与管理接口

- time_utils 新增 to_beijing(统一naive按UTC转北京时间) + working_duration_hours(排除周末/节假日)
- Holiday 模型 + alembic 迁移建 holidays 表
- GET/POST/DELETE /holidays 节假日管理接口，可随时配置放假日期

backend/app/api/v1/endpoints/holidays.py

@@ -0,0 +1,60 @@
+"""节假日管理 — 工作日时长计算所需的放假日期配置"""
+from datetime import date
+from fastapi import APIRouter, Depends, HTTPException
+from pydantic import BaseModel, Field
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.database import get_db
+from app.models.holiday import Holiday
+from app.services.auth_service import get_current_user
+
+router = APIRouter(prefix="/holidays", tags=["节假日管理"])
+
+
+class HolidayCreate(BaseModel):
+    day: date = Field(..., description="放假日期")
+    name: str | None = Field(None, max_length=100, description="放假说明")
+
+
+@router.get("/")
+async def list_holidays(
+    db: AsyncSession = Depends(get_db),
+):
+    """获取全部放假日期（按日期正序）"""
+    result = await db.execute(select(Holiday).order_by(Holiday.day.asc()))
+    return [
+        {"id": h.id, "date": h.day.isoformat(), "name": h.name}
+        for h in result.scalars().all()
+    ]
+
+
+@router.post("/", status_code=201)
+async def create_holiday(
+    data: HolidayCreate,
+    db: AsyncSession = Depends(get_db),
+    current_user: dict = Depends(get_current_user),
+):
+    """添加一个放假日期"""
+    exists = await db.scalar(select(Holiday).where(Holiday.day == data.day))
+    if exists:
+        raise HTTPException(status_code=400, detail=f"{data.day} 已在节假日列表中")
+    h = Holiday(day=data.day, name=data.name)
+    db.add(h)
+    await db.commit()
+    await db.refresh(h)
+    return {"id": h.id, "date": h.day.isoformat(), "name": h.name}
+
+
+@router.delete("/{holiday_id}", status_code=204)
+async def delete_holiday(
+    holiday_id: int,
+    db: AsyncSession = Depends(get_db),
+    current_user: dict = Depends(get_current_user),
+):
+    """删除一个放假日期"""
+    h = await db.get(Holiday, holiday_id)
+    if not h:
+        raise HTTPException(status_code=404, detail="节假日不存在")
+    await db.delete(h)
+    await db.commit()