feat: 集成 apisbo.com 中国节假日 API 自动获取+缓存

- 新增 holidays.py 服务：按年获取节假日数据，缓存到 system_config
- 区分 holiday（工作日假日）和 workday（调休上班日）两种类型
- is_working_day() 支持调休判断：周末在 workdays 集合中视为工作日
- 启动时自动从 API 刷新当年+明年数据，失败则使用缓存
- 系统设置新增「从 API 刷新」按钮，支局长可手动触发
- 支持 2010-2026 年数据，API 免费免鉴权

Co-Authored-By: Claude <noreply@anthropic.com>

backend/app/services/scheduler.py

@@ -7,7 +7,7 @@ from app.models.user import User
 from app.models.leave import Leave
 from app.models.work_plan import WorkPlan
 from app.models.customer import Customer
-from app.models.system_config import SystemConfig
+from app.services.holidays import load_holiday_sets
 from app.services.wecom import wecom_client
 from app.utils.timezone import today_cst, is_working_day
 
@@ -16,19 +16,10 @@ async def check_daily_reporting(db: AsyncSession) -> dict:
     """Check today's reporting progress and send wecom reminders to managers who haven't reported."""
     today = today_cst()
 
-    # Load holiday config
-    holiday_row = await db.get(SystemConfig, "holidays")
-    holidays: set[date] = set()
-    if holiday_row and holiday_row.value:
-        for s in holiday_row.value.split(","):
-            s = s.strip()
-            if s:
-                try:
-                    holidays.add(date.fromisoformat(s))
-                except ValueError:
-                    pass
+    # Load holiday data (auto-refreshes from API if not cached)
+    holidays, workdays = await load_holiday_sets(db)
 
-    if not is_working_day(today, holidays):
+    if not is_working_day(today, holidays, workdays):
         return {"status": "rest_day", "date": str(today)}
 
     # Get all users who need to report