feat: 仪表盘+催办在休息日跳过填报检查

- 新增 is_working_day() 工具函数，自动跳过周末 + 可配置法定假日
- 仪表盘填报进度新增 is_rest_day 字段，休息日显示灰「休」印章
- 催办调度改用 is_working_day() 替代原始 weekday 检查
- 系统设置新增「法定节假日」配置卡片，支局长可管理假日日期

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

backend/app/api/system_config.py

@@ -65,7 +65,7 @@ async def update_config(
 ):
     """Update a single config key. Only directors can change settings."""
     value = body.get("value", "")
-    valid_keys = {"notification_time"}
+    valid_keys = {"notification_time", "holidays"}
 
     if key not in valid_keys:
         raise HTTPException(status_code=400, detail=f"不支持的配置项: {key}")
@@ -75,11 +75,23 @@ async def update_config(
             h, m = _parse_time(value)
         except ValueError as e:
             raise HTTPException(status_code=400, detail=str(e))
-        # Persist to DB
         await _set_config(db, key, value)
-        # Reschedule the APScheduler job
         await reschedule_daily_check(h, m)
         return {"key": key, "value": value, "scheduled": f"{h:02d}:{m:02d}"}
 
+    if key == "holidays":
+        # Validate: comma-separated YYYY-MM-DD dates
+        if value.strip():
+            for s in value.split(","):
+                s = s.strip()
+                if s:
+                    try:
+                        from datetime import date
+                        date.fromisoformat(s)
+                    except ValueError:
+                        raise HTTPException(status_code=400, detail=f"日期格式错误: {s}，应为 YYYY-MM-DD")
+        await _set_config(db, key, value)
+        return {"key": key, "value": value}
+
     await _set_config(db, key, value)
     return {"key": key, "value": value}